well, there's +5% recruitable manpower, which is gold for manpower-starved minors. Gives a quite punch to the first battles of the operation. France can get insanely high planning bonus with GBP, over 100% IIRC. I'd use GBP as nations that rely mostly on infantry and with countries which get high buffs to max planning.
You can get the highest infantry breakthrough, entrenchment and planning bonus with it. There's also manpower buffs in there, so it's sometimes worth it as a minor. Mobile Warfare shines especially if you can get other speed buffs from military staff or national spirits, plus it gives the highest ORG for both infantry and tanks. Just make sure you take the Integrated Support side. Superior Firepower is boring but very good for any major.
