I think they mean that most operations where you might need to know the identity of a file's owner (e.g. read/write/execute permissions) will be handled automatically by the OS's security system.
Okay, so he's assuming I'm trying to read / write / execute and that I'm just overthinking the complexity of it.
I'm just doing some analysis of a filesystem and want to collect the owner of the file and see who else has permissions to it, not necessarily doing anything with the file myself.
About the only thing I can think of is to provide a personalised message ("hello mr_rustbot").
I'm not trying to get the current user running my program.