Buccal pumping is more energy intensive than ram ventilation. Sedentary, bottom-dwelling sharks generally use buccal pumping to move water over to their gills compared to more active sharks, who will use ram ventilation and swim to force water to their mouth and gills.
The movement of water for oxygen intake in sharks is dependent on whether they are sedentary or active.  Sedentary bottom-dwelling sharks rely on buccal pumping, while more active sharks use ram ventilation.