There is another use of engines at both ends. Interchange of a train in unusual trackage.
Suppose a SB BNSF train needs to be interchanged with the KCS, SB. The trackage at Rosenberg TX requires a reverse move to complete the interchange. If the power is going through, and is at both ends, great. BNSF hands over train to KCS. KCS checks train over. Now, the crew now uses what was the rear set as lead, and the ex front becomes the rear. No switching needed!