I’ve seen a lot of pics of diesel locs hauled by electric ones, any reason why ?
Speaking of the Great Northern specifically, the electrics were removed from service when the new Cascade tunnel with forced ventilation to allow diesels to operate inside was opened. So they were more of a necessity than helper power until then. The diesels might have run on the steep approaches and curves for push and dynamic braking, and to be up to speed when the electrics cut off on the fly (if they did that). Not sure how they handled train heating for passenger trains, which would also be a concern.