If you're on the same layer 2 broadcast network segment (typically some machines in a home office plugged into the same dumb switch, or all on the same VLAN), the time/effort to do this with ssh is a lot less than using wireguard to talk between two machines that are literally plugged into the same switch.

Since the typical use case for barrier is to have something like two desktop PCs, each outputting to two displays but with no mice or keyboards, and one laptop in the center, where you want to use your laptop's keyboard and trackpad to run everything.