It's worth a lot because it keeps low/mid stacks alive a lot longer than they should.. and that enables them to see more hands and fight more.. ie. On stars the add-on is at the break where the blinds are 75/150 after the break.. say you have 3K.. not desparate yet, but not great after another blind increase.. now adding on you're at 5K and can still be an impact to other stacks.. plus other people are adding on so you are losing ground to the field.. (unless you were chip leader or had a massive stack where 2000 chips are insignificant, very rare)