Users are still useful for isolation, many daemons on your system are likely running with different UIDs (or could be configured to do so) to increase isolation between them and the rest of the system.
Groups are a bit less useful (IMO), but still good for handing out access to things like device files. If a daemon should have permissions to XYZ /dev file then you add them to the group associated with it.
Groups are a bit less useful (IMO), but still good for handing out access to things like device files. If a daemon should have permissions to XYZ /dev file then you add them to the group associated with it.