Re: I've forgotten...
"the ability to respawn processes on failure."
Let's start from the assumption that a process should not fail.
If it has failed what should an admin do about it? It might have failed, for instance, because the process had lost one of its disks.
Investigating would be a good idea. In fact it's such a good idea that the correct sequence is investigate, fix, restart. In that circumstance is it a good idea to have some automated process restart it before the admin has chance to look at the problem? Apart from the impediment to investigating the cause of failure there's a chance that the automated restart might corrupt data. If the process fails on restart we have the prospect of systemd running round like an ADHD child repeatedly crashing the system.
Oh, yes, I could set up systemd to not restart that process. So why would I want to have it in the first place?