Why Locomotives on both ends?

Normally a rear engine is a pusher, on heavy trains with steep grades, some times you will also see one in the middle as a helper.  The above pic shows NS dead heading (Turned off )that rear unit

If a local turn must switch both facing and trailing point switches, with no place to run around the train for the return trip, the railroad will often put a locomotive on both ends. This gives them the means to switch all customers on the route regardless of the way the switch faces.

Thanks