On my last dive Saturday, we did a head to toe out on the RIB, but proceeded right down to the wreck without doing a long hose deployment (s-drill). There were three of us, and Mr. A was the leader and moved us right past 20' where we were supposed to do the drill. I though, oh well, and let it go. Mistake.
At 100', about 15 mins into the dive (36 degrees and just 4' vis) I got a light flash, turned around and saw that Mr. S was having a wild free-flow from his primary reg. He had his backup in his mouth, so I turned off his right post and stopped the free-flow.
But here was the rub. The hose from his primary was trapped inside his backup bungee - actually pinned uncomfortably against his lips by the bungee. I went to my backup reg, gave him my primary, unwound his mess of hoses and rerouted them properly, took back my primary (he went back to his backup) and all was good.
However, if someone had needed air from him, because his hoses were not routed properly, it would have been a total cluster trying to donate! If fact, at 100', it could have gone very badly. Because we did not do a complete check and skipped the hose deployment and s-drill.
We talked about it during the debrief, and everyone agreed that we would not make this mistake again.