It depends.
If the clothes actually improve stats or give you new moves etc then I'll use them.
If not I'll probably stick with the base costume unless I find something I really like.
The best way to do this that I've seen is in Xenoblade Chronicles X. You could equip costumes that updated your stats but you could also use 'fashion costumes' which would only change how you look. So you could still wear the stats boost stuff and wear what you want.