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.
Like I said, I can see why at times someone needs to use small pots. Computer grows, cabinet grows, small closet's used to grow, any tight area especially with limited height involved.
But if a plant's root will use all the pot size they have to grow in that pot is not over sized and after cutting my plants and emptying my 7-gallon pots there are small fine roots all the way down to the bottom of the pots and from side to side. They aren't jam packed, they are a knotted mess, but they are everywhere, there is no area of soil without at least small fine roots. If they use all the soil in a pot, then the pot is not over sized.
The roots are not so thick that I could pull all the soil out of the pot yanking the cutoff plant. A lot of the fine roots lower would break and only a bit more than half the soil would come out with the roots than held together. When I drop down to 5-gallon pots, after cutting off the plants and emptying the pots it all comes out in one mass of roots and soil. That's why I consider 5-gallon pots to be the minimum sized pots I will use. If the roots will hang onto every last bit of soil when removed, there was nothing that could be called extra space or underutilized space and definitely not a case of them being over sized.
But again I do understand and recognize that at times smaller pots are needed because of space/area/height issues and even some growing techniques and types/strains grown. But if someone does not have one of those restrictions, they should go larger when it comes to pot sizes. Maybe not all the way up to 7-gallon pots, or larger like I use when I grow outside on my deck, but 5-gallon pots anyway.