Database operations. ACID compliance. Could also be safety critical to keep your state stateful.

Here's one: https://www.reddit.com/r/announcements/comments/4y0m56/why_r...

Failure to isolate (lock-out) puppet from switching things back on during a migration.

"Lock" as in mutex? Although those don't come with a tag, which could be very handy when debugging.

Depending on the system, I think you can find out who owns the lock.

Locking files in SVN so other people can't edit them until you've unlocked it again.

I've never seen it used, and the only references I can think of was where it was just annoying, if not a risk (someone locking a file then leaving over the weekend or the company entirely).

I've seen it used in games. Often serialised assets won't be text diff friendly. Two people editing the same data will conflict and it won't be possible to merge the result. The solution is only one person checks out the file at a time.