Interlocked functions do not lock. They are atomic, meaning that they can complete without the possibility of a context switch during increment. So there is no chance of deadlock or wait.
I would say that you should always prefer it to a lock and increment.
Volatile is useful if you need writes in one thread to be read in another, and if you want the optimizer to not reorder operations on a variable (because things are happening in another thread that the optimizer doesn't know about). It's an orthogonal choice to how you increment.
This is a really good article if you want to read more about lock-free code, and the right way to approach writing it
