Sweeping leaves an area with the effect on the ground (you see a circle). You can move around while charging, this leaves several circles on the ground, so you can cover an greater area with the effect - really nice with increased movement speed. As most players don’t see the circles, especially with many other effects, I usually move around to the guys in need (Elememe really likes it) while sweeping.
Kagura is fine if you have melee chars in party - great for shino or doppel chars. Imo it should also work for all physical DD (also ranged) then it would be really nice, as for now its a bit too narrow.