These cheap gas pipe frames are the easiest to realign. Some get (oopsie) bent when someone drives the car in to the garage and squeezes the bike up against the wall.
Aluminum and carbon fiber frames are not straighten-able without destroying them for good. Cromo frames are so much stronger it's hard to cold set them.
I respace and align several frames every year. Some due to damage, mostly because I do a lot of single speed conversions on derailleur bikes. . Respacing a frame to fit a hub vs adding spacers to an axle to fit a particular frame. Just depends on the frame construction & hub. Most single speed hubs are 110 mm wide, most 10+ speed bikes are 121, 126, 130, 135mm wide. Adding too many spacers means more axle flex and possible breakage. Some frames are just too difficult to respace well.