A lot of people have spoken of the underwater advantages of a bp/w. Can I ask what the advantages are? Just curious. Also, does a bp/w improve your air consumption?
Efficiency, comfort, and relaxation all improve your air consumption. Any gear that helps to improve those aspects of your diving will help to improve your air consumption. To many people on this board, the BP/W is a piece of gear that helps improve them.
To me, there's a fairly wide assortment of benefits associated with the BP/W style setup underwater, but there are a few main ones that are the primary differentiators (for me) when compared to a "conventional" BC.
1)
Decreased restrictiveness/more freedom. Even compared to a well-designed conventional BC of the rear-inflation type
(e.g. the Scubapro Knighthawk), your chest area will be significantly less crowded and you may find that you have more freedom of movement in the shoulder area. This has a lot to do with the minimalistic harness and the fact that your BC ends up custom sized for you.
2)
Better options for weight distribution. This is especially important in cold(ish)-water ocean diving, where we're carrying a lot of weight. Having a stainless-steel backplate with a weighted single-tank adapter allows you to place ~12lbs directly-over and distributed along your lungs. This can make a big difference in how easily you can achieve and maintain horizontal trim. Additionally, because you can more easily choose how to arrange things on and off your harness you are likely to have more options for weight placement than you would with a "conventional" BC, especially one with a medium/large integrated weight system.
3)
Stability. Using a STA, I find that my tank is much more securely positioned than on a "conventional" BC (I've never tried the STA-less wings). Additionally, the lack of bulk around the torso and the custom-fit harness really helps the feeling that the gear is a part of you, and that your movements are being translated directly to the wing.
I made the switch at the end of last year, and it's been nothing but positive. I've had a few people try my gear in the pool
(including two today - one newer diver and one instructor), and everybody ends up coming away from it wanting one.