I had a very interesting conversation with one of my diving friends yesterday. He had been really upset with the dump valve on his dry suit -- he was convinced it wasn't working properly. He felt that it just wasn't dumping when it ought, and I remembered feeling that way, myself. I told him he wasn't putting enough air in the suit, and he didn't at first believe me. But yesterday, I apologized for having forgotten to give him the dump valve I promised him he could try, to see if it would make a difference, and he told me it was no longer an issue. I asked how he solved it, and he told me . . . he started putting more gas in the suit
I think the bottom line is that air in the dry suit is not something to be afraid of. It is something to MANAGE. When you are beginning, it can be difficult to manage a larger and more mobile bubble, so you keep it smaller. As you gain facility with the suit and with diving in general, you can expand that bubble, because you can manage it. To a point, a fuller suit is a warmer suit, so there's a payoff for learning to manage more air there. The suit cannot be used to manage buoyancy past a certain degree, so if you are diving big doubles, you simply have to put gas in the wing -- at least, you will if you use the weighting strategy of "neutral at 10 feet with 500 psi in the tanks". Many people diving doubles aren't properly weighted by that metric -- they are frequently not carrying enough weight to do it, which makes it less difficult to manage buoyancy with full tanks, but could be a problem in the event of anything that caused major delay or significant gas loss.
I think the bottom line is that air in the dry suit is not something to be afraid of. It is something to MANAGE. When you are beginning, it can be difficult to manage a larger and more mobile bubble, so you keep it smaller. As you gain facility with the suit and with diving in general, you can expand that bubble, because you can manage it. To a point, a fuller suit is a warmer suit, so there's a payoff for learning to manage more air there. The suit cannot be used to manage buoyancy past a certain degree, so if you are diving big doubles, you simply have to put gas in the wing -- at least, you will if you use the weighting strategy of "neutral at 10 feet with 500 psi in the tanks". Many people diving doubles aren't properly weighted by that metric -- they are frequently not carrying enough weight to do it, which makes it less difficult to manage buoyancy with full tanks, but could be a problem in the event of anything that caused major delay or significant gas loss.