The way my nutritionist explained it to me was that the protein in foods won't absorb properly unless it is broken down by stomach acid. And since we have such a small pouch and on top of that are on acid reducers for the first year, the food needs to spend as much time in the pouch as possible. Plus you stay full longer.
So for me, not drinking for an hour after meals is a small price to pay for the results i'm having.