I just had a look at the docs on sleep().
Where would you use this function?
Is it there to give the CPU a break in an expensive function?
Any common
I had to use it recently when I was utilising Google's Geolocation API. Every address in a loop needed to call Google's server so it needed a bit of time to receive a response. I used usleep(500000) to give everything involved enough time.
usleep(500000)