@V2Blast I'd suggest that when you see a typo or obvious error go ahead and fix, but if you find yourself looking at multiple edits of the same "type," particularly on the same author's posts, take a moment to either check with the brain trust whether those seem good (here or on meta, for example) or go ahead and ping the original author first.
Worst case: people disagree with you and the internet's no worse off than before you noticed the thing.
Best case: someone's grateful to you for being willing to do the scutwork of mass-editing, or someone learns something from you that they're happy…