Patching is a whole lot easier and cheaper than me having to find the time to go to the LBS to get another tube. Particularly since I always end up buying something else besides just a tube.

I recently retired a tube with 4-5 patches in it, since it wasn't holding air and I couldn't readily locate where it was leaking. I was just tired of fooling with it. But a patched tube works perfectly fine as long as it doesn't leak.