That depends. In this example, I don’t think it’s unsafe (though please let me know if you disagree!).

We’re mounting a local directory to a directory inside a container running locally on the same machine, purely as a workaround for speed issues with the default filesystem. This means we’re not exposing anything for consumption on the wider network.

Since we’re adding the /Users directory to the exports file, we’re telling NFSD that it’s ok to mount any subdirectory of /Users via NFS but we also specify that the only valid target machine is localhost i.e.

> /Users -alldirs -mapall=$U:$G localhost

If we omitted that, then it’d be unsafe potentially as we’d make it possible for the /Users directory to be mounted to other hosts.