I don't think there are any situations where you are more likely to
win by giving away forces (can you give an example?).
Of course there are situations where you are likely to suffer smaller
losses by giving away parts of your forces. Consider:
A B
1 dragon 1 chimera
10 peasants
Getting rid of the 10 peasants is going to reduce your overall losses
without measurably affecting your chance of success in the current
combat system, the 4:1 system, and the smash system.
-- Scott T.