I always dive with my snorkle. That way when I'm either swimming to where I'm going to submerge or ascending, if the water is too rough I can use my snorkle and save on air.
Also during a boat dive, after I enter the water and am waiting for the dm/instructor to enter the water. I use the snorkle while I'm at the line waiting to submerge.
Also during a boat dive, after I enter the water and am waiting for the dm/instructor to enter the water. I use the snorkle while I'm at the line waiting to submerge.