I've flown dash 8s for while...
My previous company had the APUs removed, because the weight penalty wasn't worth the convenience of extended independent power/air conditioned ops. We had GPUs and at all our regular airports, and external air at most.
My current company has to pay a penalty and one extra person to use a GPU - they find it cheaper to use APUs everywhere and accept the reduced load and extra maintenance.
It just comes down to the dollars; that varies a lot with the route structure and type of pax you have, and the union rules you have to work with.
OJ