My machine will get you where (and when) you want to go. No problem. I'm still looking for a few investors.
Could be useful. I'd like to go back and do a few things over better. (Premise of a novel I can't seem to finish writing.)
Oh, wait! It won't put my old mind back in my young body. My old body will be there shouting advice at my young self, but my young self was ignoring everyone my present age back then. Never mind.