Having no human at inserting seats is only partly helpful in terms of human labor and time saved.
Seats are usually inserted with human operated/supervised machinery. There are 4 bolts per seat and one connector.
It's possible to program machines to bolt down the seats. Tesla theoretically could do that with M3.
I've not seen a connectors manipulated by machines so far. I don't expect Tesla doing that with M3. Model Y, maybe.
Especially with the new harness vision Mr. Musk had.