It is most important piece of command / daemon available on Linux / Unix system.
It has some nice capability which is not used but need to be aware of.

@reboot        #Run once, at startup.
@yearly        #Run once a year, "0 0 1 1 *".
@annually      #(same as @yearly)
@monthly       #Run once a month, "0 0 1 * *".
@weekly        #Run once a week, "0 0 * * 0".
@daily         #Run once a day, "0 0 * * *".
@midnight      #(same as @daily)
@hourly        #Run once an hour, "0 * * * *".