TL;DR

caffeinate helps you prevent Mac OS X to go into sleep mode.

Or, in the man page own terms:

Prevent the system from sleeping on behalf of a utility.

After setting up a monitor for my Flaky internet connection, I had an issue in leaving it running while not actively using my computer - after some time, Mac OS X goes in sleep mode and the monitor stops.

This is where I discovered caffeinate, which is designed exactly to prevent this (from the command line).

Useful to remember for the future!