In the Projects User Guide, the section on "watching" a project reads in part:
When you watch a project, you will receive a copy of mail about any objects (like tasks or revisions) that are tagged with the project, or that the project is a subscriber, reviewer, or auditor for.
Empirically, the behavior I think we see is different -- watching controls mail for objects where the project is merely tagged, but (at least for revisions) if the project is a subscriber or reviewer, then *members* get email even if they're not watching. In fact, the section above it seems to agree, more or less:
Once you join a project, you become a member and will receive mail sent to the project, like a mailing list. For example, if a project is added as a subscriber on a task or a reviewer on a revision, you will receive mail about that task or revision.
Is the behavior I think I'm seeing the intended one and the docs should adjust, or is the behavior a bug, or are I misunderstanding something so that they're consistent with each other?
I've actually always found it at least a little confusing to predict what will cause project members to get mail and what will only go to watchers -- I remember being quite surprised when after the Nth time I mentioned a project by hashtag ("ask #otherteam their thoughts") I learned it didn't cause them to get notified, unlike @-mentioning a person ("ask @coworker their thoughts"). In any event, whatever the semantics are, it'd be good to make sure they're clearly described in the docs.
/cc @alexmv who pointed this discrepancy out to me after I quoted that doc for an internal user, thinking it was right -- which I guess underlines that I apparently don't have this logic quite straight in my head.