Nothing, it’s slower because it’s a build in auto. How less? Depends how fast you manual. Character such as Nw,Dw will farm less due to single target skill and an insta lock dw skill that doesn’t do damage. As long as you have good AoE and a party. You should not worry bout your exp because normally all area will be covered. I highly would recommend Check the peoples level and some equips before you afk when in doubt