Tip of the Day-space bags

As you discover that your suitcases will be full of who knows what for everyone in your adopted child's home country, consider the use of travel style space bags for your clothes. You just pack (not beyond the line printed on them), and roll them up to remove the air. Voila! You really will have extra space in your suitcase. However, do not push the bags down while holding them perpendicularly (rather at a bit of angle) to the flat surface or you'll close off the air escape valves. Why do my tips seem to have a "do not" clause in them?!