Let's say you'd done your stupid work in stupid LAB mode, then had it in your RGB PSD as a smart object. You did some more work here and there with some Levels layers, or skin layers, or whatever.
Then you decided you wanted to tweak the stupid LAB work a bit more. You edit the smart object layer ... where? In a separate window, of course. And in that separate window, you are no longer viewing the whole edit, because you no longer have your other (levels, skin, etc) layers. You're back to an old edit.
So you tweak your stupid LAB work. You return the updated smart object to the RGB PSD, where you find that your other layers no longer look the same! A levels layer that was safe is now clipping. A skin layer that was beautifully peachy is now orange.
You do not need that shit in your life.