It is exceedingly unlikely that it actually decreases FPS. More testing to average results should reveal that you are within the margin of error.
Regardless, as I said, it is important for ProBalance to be there to act when background processes become active. These problematic background loads can happen unprectably, potentially causing lags in game play.
Finally, Process Lasso is more focused on automation and giving the user full control of running processes.
As great as it is, Process Lasso is not magic, and nobody should go in expecting a huge gain in FPS, or a panacea for all ails.