The house settles and goes out of square, taking walls and plumbing with it (ironically, the plumbing will be out of plumb). Wheel in new washing machine on nice new level floor and the fun starts. Also, once floor laid, skirting boards may not fit under door frame. I wish everyone the best and as you value your sanity, don't get too close. I'm currently facing a bathroom wall that is now so far away from the frame of the house, the tap stems no longer poke through enough for the taps to be fitted. Oh how I laughed.