1: Let girls go below 0 sanity and breed them, they'll die and create human meat.
2: Hobgoblins have the benefit of being able to use as many as you like in your party. With Shamans, Champions, Paladins, Lords/Roads, you can only have one per team. Hobs are also pretty well balanced and they have few command, meaning they won't waste a ton of goblins when they get hit. They aren't the strongest units, they're just versatile and common basically. They're the upgrade to the base goblins as throw away units pretty much that can also become competent in magic. That said, you don't need to rely on them, it's just a more streamlined way to play.
Goblin Roads/Lords are all around an upgrade over Hobs really, but when they get hit, you'll take MASSIVE goblin deaths because of their high command. Generally your back up units will only be able to tank 1-2 hits whether there's 20 or 60 because of how fast enemies scale their attack up, so it's just pointless deaths to have higher command most the time.
You could sum it all up with "Hobgoblins are more efficient/versatile/easy to discard if needed" than other goblins basically. There are better warrior types though and you'll probably want to switch them out for some more serious battles. It's difficult to get their attack/magic up to the point of breaching some future enemy's defenses.
3: As mentioned above, only Hobs and base goblins can be used multiple times on a team.