stu-
It all depends upon many many things
- to borrow Old Smokey's comment, one more factor to chuck in is the maintenance cost differential between engine useage in reverse and brake wear. Some SOPs will vary according to these factors.
Clever suits/beancounters in nice offices can spend glorious hours changing policies.
It all, however, does not stop the crew doing what they need to achieve what they need. As ratarsed said, if you are looking for quick t/rounds it is best to keep the brakes as cool as possible, hence more reverse.