Pros of autoflowers:
a. No need for separate flowering/veg areas or to switch light cycles. Can run 20-0 from seed to harvest.
b. 18 or 20 hours of light per flowering day means bud mass is packed on faster than conventional strains under 12-12. More hours of light per day means you won't save electricity, but on a small plant-for-plant basis, yield can be higher than with conventional plants in a given time period.
c. Short "dwarf" plants available; well-suited for stealth "microgrows" indoors or outdoors.
d. Plants will mature outdoors during any part of year, including non-traditional times, like mid-summer. If you want to avoid rippers and busts, or harvest plants all year long outdoors, this is a good way to go.
Cons of autoflowers:
a. Smaller variety of strains available, though this is improving all the time.
b. "Best" autoflower strains are pretty good, but still aren't as good as "best" regular strains (see a above), and in fact may never be due to limitations of autoflowering genetics.
c. Can't maintain mother plant or clone plants to maintain "killer" phenotype. Can't "regenerate" harvested plant. MUST start from seed every time.
d. Since the plants have a pre-determined lifespan before they die, auto plants are limited by genetics in terms of how big they can get. They're also generally not amenable to topping, training, etc. Although yield per square foot can be remarkably high, yield per plant is generally low,
Bottom line is that autos can make a lot of sense, in the right circumstances:
-If you want to grow inside a computer case or some other ultra tiny place.
-If you want to hide a few tiny plants on your deck or in your garden.
-If you want to be able to harvest outside before the fall or run multiple outdoor crops per year.
-If you are trying to maximize yield from really small spaces, then mini sea-of-green type growing with high turnover of relatively high yielding small auto plants is probably the way to do it.
On the other hand:
-If you want/need to grow really big plants (indoors or outdoors), autos are probably not for you.
-If you are limited by plant counts, and/or need to have highest possible per-plant yields, autos may not be for you.
-If you need the absolutely highest quality "elite strain" bud possible, or want the latest greatest award winning strains, autos are probably not for you.
-If you don't want to grow from bought seeds every time, or generate your own, autos are probably not for you.