Glazing is an art and there is different ways to apply glaze and there is different kinds of glazes to use. Although I’m not an expert on the subject of glazing but this is what I know. Glaze does a few things first a glaze can hide/cover scratches, second glaze can bring back oils to paint that the UV and heat from the sun and by washing takes (if unprotected) away.
Glazing can easily be used as a fast cheap hacking detailing job that can bring about a nice job by hiding scratches defects but once the sealer/wax is gone in time and the car is washed the glaze will be removed and the scratches/defects will still be there.
The best way to apply glaze is to first use compound/polish and get the defects out and then use a machine glaze or you can use it the other way round, glaze and then polish. The best way to apply glaze is use a high speed buffer using a wool pad, why a wool pad? Because you have to have heat so the oils in the glaze will penetrate deeper into the paint. Depending on how hard the paint is? If its not a hard paint then a PC will work ok to a point. After you machine glaze QD real good. Sometimes on black paint (depending on how bad the paint is) you have to wait a week to apply sealer because if a sealer is applied right after glazing then the sealer might cause hazing do to the oils on the surface from the glaze. Glaze works real nice on old enamel paints from long ago you can even use hand glaze on enamel paints. On clear coated cars there is two reasons why glaze can be used first is showroom cars gloss second is to bring back the oils back into the clear coat from neglected aged cars and or remove the fine mico- scratches. Again I’m no expert on the subject of glazing I just know on what I have experienced myself.