some watches implement a rotating bezel to mark elapsed time; some have an extra racheting mechanism for safety.

I've read that they help u remember when you did something. Scuba Divers: Arrow goes to the minute you went under water.

Another post online said they're used to point in a marching direction, but that doesn't sound logical. Use a compass!

These are used for mathematical calculations such as average speed or distance or for keeping track of elapsed time.