Resource Bonus

Right before you buy an ally, take a look at the two numbers. the first number and the 2nd one. You'll notice that when you buy another ally, the top number goes up. like if you had 119.5/140, then you buy a cheapish ally and it goes up to 120.6/140. I'm pulling numbers from thin air, but you get the idea, right?

Look at the wording in the treasury: "Squeeze more resources from monsters" is in it.

You also know that when you hit monsters, you get resources. You actually see 2 sets of resources. The Looted Resources and the Bonus From Allies. Well, your allies will give you a bonus in resources you get from hitting monsters. Neat, huh?

So yeah, the bottom is the "Max Monster Resource Ally Bonus" and the top one would be the actual "Resource Bonus"
Make sure you get good allies, because if you get sucky ones, you'll end up with the max number of allies you can buy but no more slots to buy better ones...

**None of this was confirmed by the devs to me btw, that's just what I believe the numbers to represent based on what I looked at. I could be wrong, I could be right. I believe I'm right, but everyone makes mistakes. If I'm wrong, do correct me. I think I'm answering the question as it was asked though.**