It is used while when VIP is active. It is used in the entry screen for the Battle section. Each sweeper uses up the corresponding Energy and the item rewards, gold rewards, and Team XP rewards are given as if the Stage was completed; however, no individual hero experience points are awarded. Instead of individual hero experience points, the player gets XP items whose total XP is roughly equal to 95 to 99 percent of the total individual hero experience points that would have been obtained if the sweeper was not used. There is no difference in reward if using sweepers individually 10 times and using the "10 times sweeper" option given at VIP level 4+.
It is useful player wants to instantly use up Energy, quickly gain Team EXP, turn hero EXP from the stage into XP items, and get the item rewards. Otherwise, you can sell them for a small amount of gold.