Well that is true for some people, but SOG growers canopies aren't wider than their pots. Aside from that the issue is height, the bigger the pot the more vertical room you're losing. To people that have bigger rooms that may not be an issue, but for cabinet growers it's a big issue, room is everything. If you've only got a few feet to work with than any height you lose is gonna make for a smaller plant, smaller plants make for less bud.
I agree there's a line to walk with container size, if I had room sure I'd use bigger containers. Using smaller containers can be a bit more risky, but in some situations it buys you extra room for your plants. If you're going to use smaller containers you should find a happy medium, use as big a pot as will work. Also keep in mind that your plants aren't spending eternity in those pots, just a few months, so there's no need to over size them.