The loco (WCAM3 earlier and now WCAM2/2P) which hauls Pune-BSL Exp immediately returns back with same rake as 11025 BSL-Pune Exp after 2.5 hours halt at BSL). So, if WAG7 is sent alone, BSL will have to send another any available WAG7 (which may not be daily available) or they will have to send BSL WAM4/WAP4 with returning train. And BSL Loco Shed is already handling huge number of trains / links and Pune-BSL Exp link is with KYN ELS. Hence, WAGx loco is sent as dead loco and Pune Operations / Mumbai Control ensures that KYN Loco only hauls the train!