Hi,
The two v. three gallon is a really big controversy and that holds true for those commercial growers. I find, that most people on these forums grow for fun or personal and for friends. In most cases, and again I have two friends who each own their grow shops and they sell to large set ups; they both agree that two gallon is point blank the most bought. Then you get people coming into the grow shops thinking they know best, or always tryng to make it' like they have it right or dialed in. The GOOD news is that they generally agree on these two basic things; 1) two gallons are great since you can get six to nine plants a light. If you can average 3OZ a plant you can get over 1.5lb a bulb. Second, some people switch over in three gallon pots for summer time since plants tend to intake more water generally but even more in the summer time for several obv. reasons. A good rule of thumb amongst use growers in BC, Canada is that, get an OZ for every gallon you use. But thats just being the basics. I can get 4oz or close to, every time, with just two gallon pot. BUT thats not with every strain.
Bigger roots, equal bigger plant, thats right, but theirs a point when that rule is not applicable. That's an argument thats not happening on this forum. But here is a point to make about that; you can do better with 6 plants under a 1000HPS in 2 gallon pots than what you can with plants in 3 gallons that grow all branchy- train if you want, I mean, I help lead the lower growth, but I also train the top of the plant with the light. Big thing is, maybe you can't grow with two gallon pots but always had good growth with three gallons- than that's what works for you and the grow environment. But try to realize were people might be coming, some do this for fun or a living.
I find two gallons rock, they are a place just to hold roots, no live soil etc. I control what they eat. I also want my pots packed-root bound before flower. I always dont want to veg for 4-5 weeks. If you go bigger pots, means more veg time. If you dont veg long, you will just get a weaker root system that sits in a larger amount of soil that tends to never dry out. So if you go bigger pots, have to veg longer, but than you get more plant that does not get much light! But, again, this is one view vs. many other self acclaimed guru growers!