From the MusicBrainz FAQ on editing:
Even some constructive edits require the approval process, like adding album art to a release. This is probably to prevent vandalism/spam not involving deletions. Although I'm not 100% on which types of edits are auto-applied and which require the 7 day wait.
Edit: Maybe someone (like a mod or admin, if they're feeling up to it?) can provide a link to a table with that auto-vs-wait info spelled out. Maybe building off of this if there isn't one already handy.
Edit 2: It just occurred to me, the whole source code is on Github, I could crawl through it myself... Unless, is this type of thing configurable? Way too many LoC in any case. (Ignore me, I'm talking to myself now)