I agree with everyone here about art dolls. If the doll is not to be played with, then there's no reason to go to the labor and expense.
I have some with sewn-on clothes and some removeable...when I make removeable clothes, I do it for these reasons:
I'm creating an antique-inspired doll, trying to stay as close as possible to the original construction methods as the antiques. (Pain in the butt, too, because every seam must be hand finished, etc. yada, and snaps aren't nearly as bothersome as hand sewn buttonholes! :~P)
Also some people want to create seasonal clothing for their dolls to match the decor of their home. Some just like to have different looks for the dolls.
But of course the cost goes up...I recently had a custom order (almost finished with her) where I gave the customer the option: sewn on or removeable, and she picked sewn on. The $$ was $30 so that may have been a factor, but this isn't a doll for a child, either.
Lots of antique dolls had their clothes sewn to them, glued to them, painted on them, whatever. You're just as much a doll artist if you do this as if you painstakingly create little wardrobes. :~)