From Bitcoin Wiki
I see the advantage being:
1. I backup my wallet 2. I sent some money 3. The 'change' of the transaction is sent to a new address in my pool 4. My harddrive crashes 5. I restore wallet from backup 6. My 'change' is intact because the entire pool was restored.
2.b. I make 300 transactions .. 6.b. Have all lost the 'change' to all transactions after the 100th?
3.a. The 'change' is sent to a random (or cycled) address in the pool without generating a new address (key pair).