I use Plasti-gauge in a pinch but I have seen it tell me clearances are tight when they're not and tell me clearances are loose when they aren't. When direct measurements aren't available feel becomes VERY valuable.
You are right; p-gage can show tight or loose if things are well bent or well out of alignment, and whether the tight or loose is on the side where the p-gage is placed. Maybe I just have been lucky with blocks....