This is a wiki best practice.
To revert is to go back to a previous version and restore it, with no edits. If you are doing anything else, say restore not revert. Revert is a word with meaning in wiki governance and so you should avoid using it if you aren't actually restoring an actual prior version.
Using it incorrectly causes various policy problems, for instance with the 3RR. If people disagree about what's a revert, such a policy may be invoked by surprise and cause considerable friction.
It is necessary (mandatory on most good wikis) to indicate why an edit occurs, including a revert. A bald revert with no other edit summary is simply an insult to the person who last edited, and is never necessary. Even spam deserves the explanatory edit summary: "revert: spam" or "rv spam".