The tubes are much better than they used to be. They used to be metal (lead, at one point, aluminum later), and just crimped shut at the bottom. The crimps could fail, and the tubes would dry out, or the neck seal could be bad. Modern tubes are much better. I'm not up on what they're doing, but there are coatings for tubes that allow the ends to be welded shut, which makes them better sealed. It's been a long time since I've had a little tube dry out, opened or not. I still carry an unopened tube, because, well, they're light. It's been years since I've patched a tube on the road, too. (I carry a spare tube, and fix the tube at home or the office.)