The OAuth grant management UI (Special:OAuthManageMyGrants) contains two links per app: revoke access and manage access. The latter gives a checkbox list for the grants the app has, and the user can enable / disable them at will.
This seems like an anti-feature. It means the developer won't know for sure what grants their app actually has; 99% of the time they won't care or even be aware of this, and the user revoking some but not all grants will lead to buggy behavior (and then possibly bogus bug reports and time wasted). It also doesn't help the user who is concerned about giving too many rights to an app, since the app will have all those rights at least for a short time after authorization.
We should either get rid of partial grants revocation, or allow opting out of some grants immediately in the authorization dialog (like e.g. Github lets you do it). I'd go with the former, at least initially.