This is kind of funny to me. I had my spare in the trunk for quite a while (didn't have a problem with trunk space locally). Then, one time when my wife went on a 'long' trip with her sisters, she had me take it out (couldn't fit luggage with tire in there). I never bothered to put it back.
I agree that keeping it in the garage is fine for 'local' use. It does seem like carrying it on a 'long trip' makes sense, BUT if it doesn't fit with the luggage it doesn't help much !
Maybe we need to work on minimizing luggage !