Did a lot of windshields back in the day. It all comes down to the installer and how difficult it is to cut out the old glass. The pinchweld where the urethane sits on modern cars is invariably nicked up or worse by the cutting tool, and needs to be cleaned up and prepped for new adhesive, or the glass will not bond and your windshield channel will rust. Or worse the glass could pop out in an accident.
That’s the biggest part where the hacks cut corners, cause you can’t see it till years down the road if at all. And they usually booger up the trim and/ or bust the trim clips.