I use it for my yarn, but it does squish it a little. If you have the papers on the yarn, they probably will fall off when you let the air back in. And if your yarn has loose ends, it’ll be even looser when you get them out. It does save space, but there is a price for it of course!
You have to get a really good seal. I can sometimes and can’t others. It’s a toss up. I think I have a good seal, then go downstairs a few days later and the bag just looks like a regular old ziplock with air and all. It’s kind of frustrating! I keep the old baby stuff in them and it really helps with the poofy comforter & bumper pads and I know I don’t need to take them out for a while. I think I may do it with my sweaters this summer too.