E.g. for quick provisioning of containers or virtual machines, this is also to make sure the required directories always exist. In a normal distribution, /home already exists, so systemd-tmpfiles does nothing, but there are cases where you want to setup a standard directory structure and this is a declarative alternative to scripts with a lot of mkdir, chmod and chown.
The name systemd-tmpfiles is kind of historic at this point, but wasn’t changed due to backwards compatibility and all.
systemd has its own containers, so this is the implementation of that requirement; “virtual machines” might use this exact binary to create home, among other directories like srv and what not. Someone at one point probably said “we always need to create these when spinning up systems, maybe systems can provide a mechanism to do that for us?” and then it was implemented.
systemd-tmpfiles claims the following:
I rather think having a purge command was the issue here, at the very least it should print a big fat warning at what it does, better even list all affected files and directories. There’s no reason a normal user needs this and with the name of the binary, it’s totally misleading, which is an issue in these situations.