Attack the enemy to your advantage, but retreat before capturing the territory.
Some reason you might do this:
- keep your expensive attack units safe from enemy counterattack
- weaken a territory so your teammate can capture the ipc’s with less effort
- save the surviving units to defend from another attack
An example would be Germany strafing Yugoslavia on its first turn, so that Italy can get the IPC on its first turn. Germany can try to knock out 3 or 4 of the 5 neutral infantry, but leave at least 1 infantry as a favor to Italy. If you retreat the Germans to Romania, the infantry in Greater Southern Germany are now positioned to attack Russia too.