When I review edits, I look for a few things:
- Does it make the original more readable? If the original has a list that's clear even if it doesn't use the SE list formatting, I don't consider that to be more readable. Changing from bold to a larger font size falls into the same category. The original is still pretty clear.
- Does it make the content clearer? I don't count commas, spelling corrections and minor grammar tweaks in that category.
- Does it improve the way the OP organized what they were saying? This is harder to judge: usually the edits that I accept on these grounds have done things like properly called out quoted material, used code formatting where it was needed, and changed spelling and grammar from being nearly unreadable to something that users could actually follow.
In the same spirit I will reject tag wiki edits that are too close to spamming a product, fail to provide usage guidance in the body or the excerpt, or are largely copied from another site.
For a question or an answer edit, if I see two of the three items above, it's an automatic accept. One of the three I'll look more closely and make a judgment call. Sometimes I'll get it wrong.