Fellaz. Let me pllllllease end this debate. I have read these posts on all the forums for years looking for the answer when in reality I have done it both ways and have all the answers right in front of me. If you don't have enough light in your setup and you let your plant get too big for the amount of light you will be at a disadvantage right away. Now let's talk about clipping at the 3rd set of leaves for bushiness. If you do this you will definitely have a harder time getting light to the inner, lower sets of branches and leaves, but you will get more tops. No matter what though, if you don't have enough light you will get fan leaves that will warp and twist and canoe yet remain mostly green and slowly die away. On these leaves I have seen the individual blades turn and twist individually to face the light source, but still even when facing they will not get enough light as they are too far away or blocked by other more important upper fan leaves feeding the tops. If this is the case just cut your losses and get rid of them and face the fact you grew too big without enough light, or get yourself some more lights and wires and shit and run em all over. I know this is a lame pain in the ass though. I think the answer is if you go the route of a bushy plant and you are indoors you must begin flowering much earlier on, while the plant is smaller so it won't end up too big later. Plants can easily double in size through the flower period. If you grow one tall non-clipped stalk indoors you will most likely get a better result if you're underlit. You could have one light on top and maybe one on each side of it and be ok. I have done this both ways. One time I was growing a plant indoors and I clipped it once and ended up with 4 main shoots each of which having a top. It started getting too big and bushy for how much light I had. So what I ended up doing was trimming the fan leaves evenly off in a spiral stair case manor. I went to each node clipped one of the two fan leaves off then the next node in circular motion all the way up, but I did NOT do the main tops. When this was done it looked like a spiral staircase of leaves all the way down. Every bud on the side of the node I clipped the leaf off of was definitely smaller than the one on the side that still had the leaf. The tops were still nice and fat though. All in all I think it got me the most out of the plant as I could with the lighting I had. I would definitely say it was obvious that the fan leaves had something to do with yield and productivity. I would also say that it will push your flowering time up a little if you clip. Not too much though. Maybe a week or two. I might want to mention I am the king of low power light growing. I don't like using big ass lighting units because risk of fire, high electric bill and heat regulation concern me. I always used a 70 watt metal hallide above and two of those big 100watt coiled CFL bulbs that each supposedly uses like 40 watts. One on each side. Combined light power usage was something like 150watts. Now with this lighting I don't get huge yields anyways, but I easily get an ounce or two of some sticky shit. And I would always have clones ready to go into the flower cycle right behind the floweing mom. If you time it all right you get a good system for the cost of only 160watts and not too much space either.
If your growing indoors and lighting is not plentiful just grow a smaller plant. Begin flowering sooner and keep the lights as tight down on it as you can through the whole growth period. Make the light adjustable right off the start so as the plants gets taller you can easily raise the lights with it. Also look into a strain like LowRider. Those little bastages grow quick and short and auto flower while still producing some fat nug. You could probably grow 6 of those 1 to 1.5' tall in one pot and get up to an ounce off each in 6 weeks total with something like a single 150watt metal halide. And yes you can be all technical and switch to a sodium bulb for flower, but I never do and I still get good buds.
If you grow a single stemmed plant you will have much less trouble with lighting. I had a buddy with 6 beauties in a closet and he did not clip them so they were just tall stalks. He used 3' CFLs running vertically up and down between them all and two 4' CFLs running horizontally above the plants that he raised as they got taller. He also had tin foil on the walls of the closet all the way around. He had no symtoms of burning on the leaves as people always say happens with tin foil, but they were also only CFL lights so they are not that intense. When these got done flowering they were about 3 to 3.5' tall looking like a big fat donkey dick bud all the way up. A couple to a few ounces off of each.
One thing I should mention I have noticed over the years is that when I've grown bag seed that is obviously not pre-feminized. I always clipped them to keep them shorter and bushier and had something like 98% success rate with them being females. I believe firmly that shorter bushier plants tend to naturally go female and tall stick plants (not guaranteed feminized of course) tend to go the male route naturally. In theory the males want to be the tall skinny one so when it opens its little nutsacks to spread it's seed, the taller it is the better chance the pollen will get up in the air and spread further and better. The females want to be short and bushy with lots of surface area and seed producing locations to catch all the pollen fall out. This is not a fact, but it is an observation I have made over the years. Only one time I had a short bushy one come close to being a male and it was stress related. It was growing in a basement and it was winter time so the basement was like 55 degrees and lower sometimes in the room it was in. It was already showing female flowers and then it started showing some male balls in there too. It was going hermie on me. I bought a ceramic heat lamp and pointed it at the pot to combat the cold and keep the roots warmer. Keeping the roots and soil warm was key because at least the roots will feed the warm water in the soil up to the plant that is cold because of the air temp. Meanwhile I was plucking the nutsacs off here and there as they would show up. In no time they began to stop showing up. There was a couple left on the plant that I missed before. I plucked them off and I happened to squish them in my fingers and look inside and I swear I saw a female pistil in it. I may have been wrong, but it appeared that way. Either way the point is the one time I had a bushy short plant going hermie on me and I corrected the cold issue it went right back to being 100% female and the male flowers quit showing up. It fully flowered and was good seedless bud. I acted quickly, though, in correcting the problem. This is key
All in all. If your leaves are not drooping and wilting then don't clip them off. Some of them will normally eventually yellow and die during the flower. When they do, pluck em off. This is normal. If your leaves are droopy, curling, still green and you are sure it's not anything other than a lighting issue, meaning you went too big for your light and area, then just clip the messed up leaves and accept the reduced yield and understand the yield is just equivalent to the energy and space you gave it anyways. You will still get some some nug out of the deal. Just make sure to make clean precise clips of the dead or underlit leaves. This way you won't stress the shit out of it or disease it. I usually squirt a bit of fresh tap water on the exposed flesh where it was clipped with the idea the chlorine may help keep the area germ free. Either way I have clipped many many leaves and never ruined the plant. Only affected the yield a little and maybe length of grow time. I have even clipped all the fan leaves off during flowering and only left all bud leaves and small newer fan leaves and the plant still budded out, but definitely with a lesser yield.