ekewaka:Inflating the bc and drysuit would only be necessary while descending. Why would you be descending while sharing air?
Divers distracted by sharing air, not paying attention to their buoyancy might descend (unintentionally) in the water column while they are initially starting the Air Share. If your buoyancy gets off in a drysuit, and you start to get a squeeze, you can drop quite rapidly (which is believed to have played a factor in the death that took place at Gilboa during the DUI demo weekend in 2003).