That's useful information Mike. I am a bit curious about what the most
common use cases are for atomic increment/decrement. I'm familiar with
atomic add as a sort of locking mechanism.

They're useful for caching denormalized counts of things. Especially things that change rapidly. Instead of invalidating the counter whenever an event occurs that would incr/decr the counter, you can incr/decr the cached count too.

In the case of Cassandra, they're useful for keeping counts of things in general, since there's no efficient way to perform count operations with Cassandra.