I dont use them, but I can see the validity.
1) I, and many fellow hunters, are strapped for cash. That usually means we own precious few guns. If I have an '06 bolt action, and I have a kid or young lady Im introducing to the sport, its much chepaer to go reduced loading than buy new guns.
2) I admit it, I own a .30-06, I just HAD to have one. Touted as the king of game cartridges it can drop game at 500 yards in well trained hands..........problem is, here in NH Im hard pressed to find clearings over 150-200 yards. So this is WAAAAAAAAAY too much gun for the intended purpose. Well, with a reduced loading Im not beating myself up just because I own an '06.
I could go on, but I hope you get the idea.
Brian