If you've ever shot a wedding with multiple cameras, you probably know how important it is to synchronize the time between your various cameras. If your cameras are out of sync by only a few minutes, the timeline of events your images show (when sorted by time captured) can be jumbled and confusing.
The solution? Use EOS Utility to synchronize your cameras' times with the time of your computer.
Directions for EOS Utility 2.14.1 (EOS Rebel, xxD, 7D, 5D Mark II)
Directions for EOS Utility 3.0.0 (6D, 5D Mark III, 1D-X, 1D-C)
There is also an option to automatically synchronize the camera's time with the PC whenever it's connected. You can find that option in the EOS Utility Preferences window.