You will find, if you have a plant in a plastic 12oz cup and it is growing really well, that if you then transplant it to a 3-5gallon pot of medium, it will quit growing and just sit there for a period of time that could be as much as a couple weeks. The reason is that the plant has paused its veg growth so that it can grow the root mass. Once the root mass has reached a stopping point, then the veg will take off again. So it doesn't matter a whole lot about "root bind" in smaller pots versus "root freedom" in huge pots.
It is a factor that very much affects the plants, but you can grow a nice plant in a 2ltr bottle and watch it get seriously root bound, and if you feed and water it properly, it will still grow and produce quite nicely. I once grew a plant in a 16oz plastic dinner glass as a part of a contest and that one plant produced 1oz of dry bud.