In large scenarios where lots of battles can/will take place, a lower MRPB setting can reduce the risk of early turn ending before all your planned combats are resolved
I've played some scenarios vs Veers, with an MRPB setting reduced to 3
If I understand well, that enables you to have less surprise and to better control the unfolding of the engagements.
Yes, MRPB at 10+ makes for an unpredictable game where one battle launched at turn start can last all turn and burn it all. It may be "realistic" at a small scale (ie 1/2 day, Coy sized battles), but when you play entire East Front or such it's totally ludicrous...
With MRPB at 3 you're sure that whatever happens you'll get 3 impulses (rounds 1,4,7), battles will only burn 3 rounds max.