The only scenario when you don't add on is when you are really short and the add on doesn't keep you up with the blind structure. I'm sure there could be some insane scenario where an add on would be 1% of your stack but even if this is the case I don't think it is mathematically wrong to take the add on, it is however wrong if you are extremely short.
I think you have a thread about this in the 2+2 library where some guy go to great length to explain this if you don't believe me.
Quote:
Originally Posted by zHuckFinnZ
I dont always add on. In my local casino the pay out structure isnt that great, so to maximize my ROI, I dont want to invest as much. Our tournament offers 1 rebuy and 1 add on. Some people choose to play super aggro with first buy in to build their stack. I tend to sit and pick them off to build mine. If I am average stack or below, i will add on to give myself a chance. But if I am near the top I wont. I know I can take advantage of these guys this early still. But the blinds go up so fast, within 1-2 levels it wont really make a whole lot of a difference as you are gonna have to get it in anyway.
I'd say you do wrong if you act like this. Keeping up with the field is probably more EV then saving money by not adding on. You already have money sunk into the tournament and what you are paying for is to
"keep your part" of the prize pool. If you don't add on you will give up the
'cumulative value' of going all in and doubling up.
It may be marginal in some cases but I doubt there are many cases where this is true.