Ive known people do that, they know in 6 - 12 months time granny might be moving in, so just run the waste and fit a toilet if they do, even known someone fit a washing machine in the corner of the room, so the waste and pipes are run
talking of neighbours, i know of someone who was convinced his next door neighbour would grass him up, so as he was in the planning stage ( not planning permission ) he moaned to the guy about the cost of architects and the cost of planning and said he had just been charged this and that for the plans and to submit them, the power of persuasion