It's there to calm guests down - simple as.As in the case of B&M coasters - which use ratchet systems for most restraints - there's no physical way of releasing the restraint mid ride. Every single ratchet would have to be completely worn down for it to fully open - by which time, reports of the restraint opening slightly would've been addressed due to guests continually telling the staff/the staff noticing whilst checking restraints.I'm sure most people have experienced an inbetween ratchet ride - where the restraint moves a few cm. The seatbelt just reassures the guest that if the restraint opens further (which, 100%, it wouldn't) they won't fly to their death.