I dont know whether there should be a stop at Chandrapur. Chandrapur is the district HQ and the population is about 6 times that of Ballarshah. There are many new factories near Chandrapur. I would call Chandrapur normal passenger halt
Ballarshah is basically a technical halt..It is the last station in the Central Railway zone for Indian Railways. Hence all the trains entering South Central Railway zone stop here for Crew Change(TTE, Loco Pilots, Guards, RPF) .. This is why there is a 10 minute halt as compared to 1 minute for Chandrapur as far as AP Express goes