I've seen bikes with a couple of inches of spacers above the stem while the owner decides where they really want the bars but that's strictly a temporary measure.

I always leave my steerer about 10 mm longer than I need and use a 10 mm spacer above the stem for two reasons: 1) to assure the steerer is completely supported inside the stem, particularly for carbon steerers and 2) to give me a bit of adjustability if I decide I want the bars slightly higher in the future.