I don't quite understand some of the other reviews; they indicate they were using these bags for long term storage. These specific bags are travel bags, used to help reduce the bulk of your clothes when travelling. They aren't intended for long term usage and because they are meant be rolled to squeeze the air out, they aren't tightly sealed.
All that being said, these bags are useful but have one particular quirk. If you truly roll these up from the zippered side, the clothes tend to bunch at the other end because they slide. We have found that rather than rolling, it is better to lay the bag on a firm surface and lay down on it slowly. However, that is not nearly as quick or convenient as rolling them and as such, makes them less likely to be used more than once or twice for the purpose of reducing bulk.
There are some positives regardless of the amount of air you squeeze out (or don't squeeze out as the case may be); these bags are heavier duty than regular ziplock bags and can be used to store items to keep out dust, mildew, etc. They are also useful when travelling when you are likely to have wet swimsuits, towels, or other items that you need to keep separate from your other clothes.
I rated these bags 3 stars due to the rolling issue I mentioned above; it really takes away from the ease of use and original intended purpose (to have your clothes take up half of the normal space). Sometimes this product (or other versions of it with different numbers of bags) is part of Amazon's 4-for-3 promo, so be on the lookout.
As a side note, I do use the regular non-travel space bags with on issues and find them to perform exactly as they are supposed to even after years of being in storage.