1. In general, other people's WIPs should be left alone until approved. It's okay to fix links and typos.
2. If you're the reviewer, you can edit for links, format, spelling, grammar, style, header levels, and (within reason) adding events that happened in the RP that help history sections, etc. In other worlds, technical stuff. In general anything with the content/context/meaning you should ASK the submitter to make changes if they're needed instead of doing it yourself, or ASK the submitter if it's OK to change something in the content. Staff can also tell people to change things, if they go against canon or are against the site rules (nsfw content, etc.).