Knowing the correct time is often a matter of life or death – why? Imagine meeting with your wife and her watch is 20 minutes faster than yours. :)
In computing terms, it is also crucial to have your system time calibrated against a standard. There is a network protocol that handles the synchronization of system clocks and that is the Network Time Protocol (NTP). In my personal home network, all three computers sync to an NTP server overseas. Whilst this is an acceptable setup, imagine having 50 or more querying an NTP server outside of your network – then the traffic, whilst relatively small, can be significant. You may want to think of setting up your own NTP server. Linux-watch.com (no pun intended) lists the steps needed to setup and configure your own NTP server on Linux.