How does the sticky bit help at all?

The way I understand the sticky bit on directories is that only the owner of a file within that directory can delete the file, instead of everybody with write permission. I don't get, though, where that would be actually useful. If everybody can still edit my file, including just deleting all the contents, what scenario is there where the sticky bit actually helps? I have read that it is used on /tmp, I don't get why that is either.