I fold it and keep it in my BC pocket.
As a brand new diver, I found it to be annoying. When I read on SB that many experienced divers did not dive with their snorkels, I felt like it validated my limited experience, so I stopped diving with it attached to my mask and kept it in my pocket.
I actually took it out of the pocket and used it last summer.
It was a boat dive off the coast of New Jersey, planned 55 feet maximum depth. Seas were relatively calm with a light current at the start of the dive.
Late in the dive, the current at depth changed direction and increased significantly. When my buddy and I followed the wreck line that had been laid on the bottom back to the anchor to ascend, there was no longer an anchor. After I made sure we were in the correct spot, and after I realized we did not have an anchor line for our ascent, my buddy and I began our ascent. We took it slow and did a safety stop.
During the ascent and safety stop, I had no idea where the boat would be when we surfaced. I figured the boat would hopefully be nearby and keeping a lookout but I also knew that there was the potential for being in the water for a long long time.
At the completion of my safety stop, I had about 750 psi left in my tank.
When I surfaced, the seas were pretty choppy and I could not see the boat anywhere nearby.
I decided I'd breathe from the snorkel in my pocket instead of my reg so that I would keep the gas in my tank in case I needed it. I didn't know if I'd be in the water for just a few minutes until found by the boat, or for many hours.
I had an air powered horn on my inflator hose, so I wanted to have the air in my tank to use the horn over a long period of time, if that became necessary.
So, I used the snorkel to conserve the air in my tank for what I thought were other potential needs. I was glad I had it with me.
Michael