What time do you wear?

Hey I have a question for the watch experts.

I am a watch noob.

It seems as though many of the $$$ watches such as this Omega Seamaster that I like... :
http://www.omegawatches.com/index.php?id=557&pos=7&no_cache=1

...have a "rotating" bezel with numbers on it.

Can someone explain what function this serves, with a specific use case outlining a scenario where someone would use the rotating bezel to serve some purpose?

thank you!!

Yes that makes sense, thanks ( :

I'm probably not going to be doing too much diving, but I suppose that could be helpful with not burning the brownies. I'll probably burn them anyway, though