I've ripped out the floor of my bathroom down to the joists. The bathroom is 5 ft x 4 ft. Should I use tongue and groove or can I use standard plywood? Does it matter?
Depending on the direction of the joists, it will only take 1 sheet, the T&G will have no value, unless the floor you pulled up was T&G as well, then it will only help on one edge.
If the T&G was cheaper than square edge, then I would use it. I have seen it cheaper in a big box store, although I could not figure out why it was. It was not on sale....
There are advantages to using t&g.
In terms of substrate requirements, it doesn't matter. A 5/8th sheet of t&g will support the floor just as well as a 5/8th sheet of standard.
For your considerations, with standard you'll have to space them with a 1/8th gap between sheets for expansion/contraction, this isn't a problem with t&g, they can be tightly fit.