In a collision, a damaged seatbelt can sometimes break. Is it likely? Who knows, but is it worth taking a chance? I remember working on GM cars back in the day and they even warned against using chemicals to clean the seatbelt (especially bleach) as it can weaken the threads that make up the belt. This obviously would not become apparent until you are in an accident and it snaps.
Cheaping out and paying minimum wage wasteoids to mount tires, rotate wheels, or perform alignments (aka loosen and retighten bolts on major suspension components), and service brakes is.... ~10,000x more likely to kill you
Or even just buying a new vehicle assembled by morons will do the trick, too
And tons of people --- hell, MOST people --- do it, then tons of people get hurt or die in "idk wth happened" accidents.
But life goes on....and oddly, most people survive for an average of 70-some years.
Btw, remember that just because YOU'RE not getting ******* discount maintenance does not in any way shape or form protect you from the guy in the next lane and his poor choices.
Life is full of scary shit. Deal or go hide in a bunker.
PS seatbelt or seat snapping in a collision won't actually do much harm in most cases. The energy will be absorbed by the force of the "snap", much like a crumple zone