Warlock – “Expansion” [4th campaign, 2nd mission]

Well, if we're talking specifically about this mission, you start with a practically fully built Castle (except for the Witches and Dragons), so it's hard to say that it allows you to double your army. In general, though, starting with a strong base can be a big advantage, but if you don't want your additional hero to be killed by the first enemy you encounter, you have to give them some of your army, which means sacrificing some of your main hero's forces. However, I did hire an additional hero to capture mines and gather resources, but usually, my loyal (well, at least for a while) squire, Shadia, did that job.