When installing FreeBSD (or NomadBSD) to the machine’s internal drive, there is the choice of file systems to use, either ZFS or UFS. The latter (UFS) is the Unix File System, the FreeBSD standard for a good many years, and Nomad’s default file system. The Z-File System (ZFS) has a number of advantageous features over UFS. You can read more about it here:
‘https://www.freebsd.org/doc/handbook/zfs.html’
For installing Nomad to an external USB flash drive, best to stay with UFS (the Nomad installer’s default).