Holley Secondary power valve ?????

Advantages and disadvantages? My HP 750 came equipped with one OOTB on primary and secondary blocks, but I have always blocked the secondary PV in the past. For a mostly street driven 416 I'm trying to decide if I want to try one out on the secondary block or not. I have already done a jet swap to 76p/84s and am on the edge of putting a 50cc accelerator on the secondary side. I have only dealt with single power valve carbs in the past, so I'm leaning towards blocking it off. Anyone have a good reason as to why I should use one or not? If 2 are run should they be the same sizes or set in stages? Im kinda shooting in the dark until I get it fired up, I'm guessing vacuum may be 12-14 so I temporarily started w/ a 6.5 on the front block. Any advice and or experiences welcome.