Which rewards get compounded?
Currently all the farms get compounded except for the BUNNY Staking farm and the BUNNY/BNB farm. The BUNNY rewards that come out of all pools, currently are not compounded. Only the CAKE and flip rewards are auto-compounded.

Why is there a Claim Button on Auto-Compounding Pools?
The Claim button is an extra option for those that wish to use it. It was a suggested and voted on by the users.

All pools that have “auto-compounding” or “compound cake recursively” in their description are auto-compounding the profits. The BUNNY figure that appears on the Profit line is what you would receive at the moment you choose to Claim.