Originally Posted by FBinNY

I guess I should have completed the thought. You only buy one spare tube and carry that. But you don't discard the punctured tube. You put it into your bag, take it home and patch it at your leisure, then it becomes the spare.

So other than the initial spare, you're still patching and reusing tubes, the only difference is you're doing it at home instead of on the road, where it might be raining, cold or dark.