I think it's a little unfair to remove this and the similar warning [about running the daemons] back on line 22.

I think both of these warnings date from a time when running the daemons was optional. Long ago, we'd send email in-process if you weren't running the daemons, and most of the other stuff that only happens in the daemons didn't exist yet, so you could have an almost-fully-functional install with no daemons. Both messages are calling the queueing behavior out as exceptional in case you aren't running taskmaster daemons.

Now, daemons are mandatory and a lot of stuff (email, feed, repositories) simply doesn't work if you don't run them so I think these warnings are probably no longer useful.

Particularly, this mimics bin/search index [--background], which I don't recall seeing confusion over.

I can see that this comes from PhabricatorRepositoryCommitHeraldWorker, but maybe it's a good reason to separate these workers?

Is there a specific reason this motivates separation (e.g., a chain of events where separating them leads to a better outcome than combining them, specifically because part of the workflow may be slow)? The only thing that springs to mind is that if the "Owners" step has some kind of call which is likely to hang/time out, we'll kill it sooner if it's separate -- but it doesn't have anything like that AFAIK, and killing it sooner doesn't really matter much since it will just retry anyway.

(Separating them also lets us apply owners/audit changes as soon as they're ready, but I think this is actually sort of a bad thing: if there's some kind of issue with pulling the diff, it's probably better that the whole commit stall than that half of the process work.)

so these will tasks will permanently

Er, these tasks will fail permanently.