AfterDark
Contributor
On some dives like @Bob DBF posted having a snorkel to use can be an asset. I was so accustomed to wearing a snorkel I've got a picture of me wearing one an ice dive! Just forgot to take it off, someone asked me if I was going to make a hole in the ice for the snorkel. 
Cave and ice diving doesn't offer many scenarios where a snorkel is useful so why take one?
Shore diving certainly offers a plethora of scenarios for using a snorkel. Last week I snorkeled over 200 yards in 10' of water with 20' vis quite a pleasant way to get to the dive site, much more interesting than looking at the sky while swimming on my back.

Cave and ice diving doesn't offer many scenarios where a snorkel is useful so why take one?
Shore diving certainly offers a plethora of scenarios for using a snorkel. Last week I snorkeled over 200 yards in 10' of water with 20' vis quite a pleasant way to get to the dive site, much more interesting than looking at the sky while swimming on my back.