I don't know how you work in the studio, but when I get a rhythm with my subject, I sure as hell don't want to have to stop everything just to swap out batteries, and fussing with recycle times, not to mention the lack of power with speedlights, they're just not fast or powerful enough.
I've tried using speedlights in the studio instead of AC strobes, and it's a disaster by comparison. an SB-800 for a hairlight or something like that is fine, but as the whole set up? no way, it sucks.
Speedlights are amazing for working on location, you can fit them in your pocket, no wires, clamp then anywhere, but they have hardly no buisness in the studio when shooting people or even product compared to AC strobes.
Anyone on here who shoots in a studio for a living and not "just to sort of dink around" will agree, speedlights in a studio are a waste of time, money, and batteries.