Less xp, no control over quality, if you're in a situation where the xp doesnt matter, you would be better off just handling the synth on your own and HQ what you're making.
Its great for a break from the game and need supplies like leather for future crafts get a stack of 99 (if it goes that high) set it to quick synth and come back later
I use it to make bulk mats even though I'd get slightly better XP from them, the mass mats I need are pretty low XP vs the time it would take it's well worth it.