I've grown 2 plants in a pot a number of times and never had any problems whatsoever.
I've 2 and 1 right next door with little difference in yeild per plant, actually i could argue some done better 2 in a pot.
One issue with multiple plants in a single res is that the roots intertwine and that
can be an issue if one plant has to be harvested early. If that does happen, the way to deal with it is harvest that plant but leave enough foliage on it so that they plant is still alive. That allows the roots to stay alive, as well.
Re. yield - I think it's fair to say that, unless you come up with an extreme example, the "ideal" number of plants is the number of plants that it takes to fill the entire grow space. For the last few grows, I've only grown one plant but haven't filled out the grow space. One reason is that I use a veg light, which results in shorted plants but, even after topping and LST'ing as best I could, the plant was 30" x 24" (front to back) so I had 18" "unused". Sure, I could have used the flower light, instead of the veg light, and maybe made it a little wider but that would have also made the front to back measurement too big to fit in the tent. For my current grow, I'm going with two plants in a 2' x 4' and that should "fill the entire grow space".
At the other end of the plant count argument is the argument that Mr Growit makes in his video "Why I grow small plants". He presents some really solid arguments, the best being that growing, say, 4 plants in s 2' x 4' means that you're able to fill the grow space but, because the plants are smaller, you flip them younger, and, as a result, your grows don't take as long as a "regular" grow. I can't fault his logic there. That also has the advantage of allowing a grower to grow different strains, so, overall, I think he's on to something.
"better 2 in a pot" - no argument from me!
