With no reads I will usually peel down at least 2 streets with weak pairs, and at least one with A-high and K-high, just to prevent my flop folding range from becoming exploitably high. You normally shouldn't do that in very coordinated boards where it's hard to balance a bluffing range anyway, but in dry flops, definitely peel flop and peel turn sometimes, and fold river. Also, anyone halfway-decent is doing this as well, so if you check down two streets you can bet at least one for value with ANY pair.
If your opponent is playing too passive post and not bluffing enough, you can start exploitatively folding bottom pair and A-high hands, or turning them into bluffs.
In most SNG/tournament HU situations though stacks are too short to profitably peel 3 streets. You HAVE to make the decision, either pre or otf, of whether to GII or fold.