It allows you to sync between 2 machines (bi-directional) over TCP or SSH.
Note that TCP way is not encrypted, you may use wireguard as transport layer encryption for that purpose...
You can use an external application to copy if file size is larger than an arbitrary number. (Eg: use rsync for files > 1gb)
that said, i haven't managed to set it up for my android phone yet - it's not available in termux and i have NO idea where to start if i'd like to package it myself. probably has to be done by someone who knows ocaml, since termux' environment is so different from normal linux.
unless... maybe i should give proot a shot (chroot in termux, lets you run something closer to linux). but it's another layer of complexity on top of everything....