Unlimited re-buys create weird situations. For example, one night I hadn't rebought, they are paying 3, and 4 are in. I got riverred and KO'd. A re-buy was 10BB. If I rebought, I would be in dealer position. Chip leader in SB, BB had about 10 BB, but would have to pay the SB next hand too, so he'd be down to 7BB before I had to pay. UTG had about 8 BB, and would have to pay 2BB before me, and 1BB when I had to pay a BB.
I wouldn't normally consider rebuying in that situation, but basically I was assured of finishing in the money, and coming out ahead. I re-bought. I finished 2nd -- one of the others was out before I paid a SB, and the other had less than 1/2 my stack.
I benefitted from those rules, but pointed out how absurd it was that I could do that. I could also have pointed out how absurd it was that the other 2 had rebought, one that round, when they were getting 15BB or 10BB. If I weren't playing behind both the low stacks and both of them didn't have to pay a BB before rebuying, my math wasn't nearly as favorable.
Most re-buys I've seen require a player to decide immediately whether they will rebuy.
When we do re-buys, they end 2 hours into a 4-hour game, or 2:20 into a 6-hour game.