It’s a lot easier and cheaper to erase a few lines on a drawing than it is to tear down a wall during construction. Thorough documents result in better budgets and more accurate bids. The more that is on paper, the happier you will be in the long run.
If the project has a faucet or cabinets, etc., etc., you’re going to have to pick them out sometime. Do it during the design phase and the construction phase will be less frustrating and more efficient.