Almost every pair of bib's that I've owned has come with belt-loops so you have that option (to cinch it up with a belt). Otherwise, I think the only problem you'll have (and it's really not that big of a problem) is that you'll lose heat and run the risk of having snow get into your pants (not all the time, but it seems to happen at the worst times if it does happen at all) if the garment is too loose. Plus, who wants the upper part of the bib floating around extra loose under your jacket while you're riding - imo that wouldn't be comfortable/convenient especially if you like to get in/out of your inside jacket pockets all the time.