My spare room was literally floor to ceiling of boxes, and now it is clear and my study.
I've always just moved stuff around as I moved house, but this time I was utterly ruthless. Open up a box, have a quick scan through, if nothing jumped out at me as needing saving, the whole box went in the rubbish. Very cathartic, I can highly recommend it.
A year later and I haven't missed anything that was chucked out.