They are small enough it's worth having one in the seatbag. Even if you don't end up using it on the road.

And those rare times when I have had to patch on the road I don't have much trouble finding the leak, you just hold the tube in front of your face and pump it up, feel/listen for the hiss.

Actually I somewhat enjoy patching tubes. If I am on a group ride I use a fresh tube, but if on a solo ride and in no hurry I will often patch instead.