"How much storage do you really lose?"
Hard to answer. But our cabinets go FULL wall to wall.
I think if everyone went into buying these rigs and forgetting having a 4th slide is a biggie and forgetting it is quite a price bump MOST would get the NON slide Vanity. ONLY negative to not having it is less space between the bed and the Vanity Cabinets.
Maybe someone can post similar pics with the Vanity slide.