X mentions Experience Is A River, which works an exp "trick" basically the same way.
LA+1 and you reach 4th level.
You are 3rd level + 1LA, the rest of the party is 4th level.
You LA Buy-Off.
You are 3rd level +
OLA, and you don't need to mention LA anymore.
You are 3rd level, the party is 4th level.
You adventure and gain exp, but you gain it
faster because you are a level down.
You are 4th level, the party is 4.666 level. (faster exp rate here)
You are 4.333 level, the party is 5th level. (same exp rate here)
this pattern repeats, but the easy math is 2/3 exp ... so I'm shorthanding the rest of it.
You are 5th level, the party is 5+(4/9) level.
You are 6th level, the party is 6+(8/27) level.
You are 7th level, the party is 7+(16/81) level. (if you round it to 16/80, you get 1/5)
You are 8th level, the party is 8+(2/15) level. (1/5 * 2/3 =)
You are 9th level, the party is 9+(4/45) level. (if you round it to 1/10)
You are 10th level, the party is 10+(2/30) level. (if you round it to 1/15)
So at this point you are less than 1 encounters worth of exp behind the rest of the party.
1/13.333 is the ~approximate game math. Basically you've caught up.
You might have been awarded more/less/different exp depending on party situation.
At or during 11th level, you are less than 1/2 an encounter behind.
And you got a "free" LA's worth of goodies.
Maybe it was worth it.
If you have LA+2 it starts at level 6+2=8.
There's an extra buy off level in there.
It delays the catch up by about 1 level.
Maybe it's worth it. Sometimes it is.
You get to do the math on that one ...