Actually the most important thing has been already said:
If you already invested money in the tournament its highly +ev to buy yourself another piece of the prizepool. Look at this like this:
At the beggining of the tourney you pay, let's say $6.69 for a share of ~$1.2k.
If you rebuy at 75/150 you buy yourself a piece of ~$1.5k for 6.38. Bargain!
Also, the pure profit comes from ppl who left before addon. Imagine the tournament: 150 man turbo + $200 added! Bargain again!
The rule is simple: the closer to addon the more profitable is rebuy.
In terms of double/single rebuy its actually a matter of taste. Recently I have been experimenting with single rebuys and for + surely are:
- lower abi (mine was around ~$8.5)
- lower av duration time
- easier decisions (less postflop play, especially vs regs)
There are also downsides:
- not getting max value vs weaker players with double rebuy
- smaller $/game
What needs to be considered is your hourly. I think this is the only thing that matters. With single rebuy your true roi will be probably higher than with double but your $/game is it should be calculated like #games per hour * $/game.
I personally prefer deeper stacks so double rebuy is the way to go
BTW, I dont think these games are very soft, as many ppl say. Yesterday I had a sng with 20 left where 16 guys were regs. Still, if you work hard enough and play solid the game is one of the most profitable around.
See you at the tables