I learned by experience the hard way that you don't need a snorkeling snorkel for diving, meaning my regular dry snorkel that doesn't fold up. In my early days, after my mask was leaking and fogging up so much, it was suggested to me by someone more experienced that having a rigid snorkel attached to your mask creates a bit of a drag or resistance on your mask thereby breaking the seal around your face. Problem solved. I no longer dive with a snorkel attached, but I have a cheap rollup snorkel ($11 USD on Amazon) in my BCD pocket for the "just in case" situation on the surface. I always travel with my snorkeling snorkel on the boat. There are some occasions during a surface interval that you may get to snorkel. A couple of years ago in Cozumel, during our surface interval, a friendly sea turtle was hanging around our boat, so I slipped quietly into the water with just my mask and snorkel and had a close interaction with this sea turtle. It was pretty cool!