In IR, that too between zones, most of the times it works on mutual benefits. something like, SR if agrees for mrng arrvl, evng dep, would not be ready to take PM. in that case PM.should be done by CR itself.. but slot might not be avlbl at cstm.. so rsa wth siddeswar.
cmng to swr, a new terminal has opened up which have ample scope for PM of new trains, so if udyan is shifted to swr, cstm gdg can be given rsa wth udyan. cstm gdg is again a train from swr territory which can now get advantage of getting full rake unlike 12 coacher right nw.