Do tampons make u bleed less?

When I dont use tampons, I bleed for the full 5 days & they are really heavy! When I use tampons, I only bleed for 2 - 3 days & the tampon doesn't even go completely red (as in it's not filled to capacity). How can this be? Is it some kind of gravity effect, like when u have a tin full of water but oy a small hole & so it doesn't come out at all unless u put another hole in so air can replace the water that's coming out? It's really weird! Or is it because the muscles are loose when I'm not wearing a tampon that they allow the blood to flow freely? I do have problems with my period, like I get them irregularly, sometimes only once a year! I have POS (polycystic ovarian syndrome), but there's nothing they can do about that. :(