Cafe41-I think the worst thing that can happen is when you develop blisters. This is so uncomfortable. This sometimes even happens to me with new sneakers.
I think that if the sneakers are slightly loose, then I will probably develop blisters. It is best to buy sneakers that are your exact size and not a bit larger.
The shoes rub up against the skin; let’s say when you are running which is why the blisters develop.
I learned this the hard way and now I stick with my size shoe rather than a slightly larger pair.