From the back of the box:

Use smart bombs, samurai hogs, scare tactics, and other nefarious methods to out-manoeuvre and out-demolish your opponent.

The heavier fire you use, the stronger the weapons you leave for your opponent. The bigger the bomb, the more likely you'll hit your own hogs. But friendly fire doesn't matter all THAT much, just as long as your troops are the last ones standing. The rest are just Acceptable Losses.