You can use a smaller pot with a larger plant you just have to water more, and possible poke a few holes in the top of the soil and around the sides and what not.
You get a larger plant faster using a bigger pot though...
I find that a 2 ft indica needs at least a 3 gallon pot, but I can but a 3 ft sativa in a 1/2 gallon pot without any issue...
I have only grown autos once and I was not terribly impressed, but as I mentioned before a plant can grow and be alright in a small pot, but in a larger pot it grows faster, and autos are like a ticking clock continually working both for and against you...Against you because any errors don't have time to right themselves, and for you because harvest is never too far away.