<Snipped quote by Tyler>
NPCs are away so characters don't get completely stuck or not know what to do next, it's filler in case the rp slows down. Also Jake and Mars are different in some ways, Jake's more of the insulting one. Also I find it bland if all characters have to have likable personalities.
I didn't suggest that Mars being unlikeable was a bad thing. S'tann is largely unlikeable and yet he is among my favourite characters; likewise Amethyst.
Regarding use of NPCs: of course they can be used in that kind of situation. But having your character surgically attached to an NPC for emergency writing shortages seems like a lazy way to handle difficult situations; plus, it's clunky and means there's this omnipresent meathead whom nobody quite knows what to do with. You might as well just make a separate character entirely if you were to do that.
However, I would personally suggest you not underestimate the value of giving your characters some alone-time. It lets you explore a side of them that they would ordinarily not express when around others.