There have been a few threads about this in the past. I think quite a lot of people like to have a pocket camera for the times when they don't want to carry a DSLR, although phone cameras seem to be taking on this role too.
I only take my DSLR when I know I'm going to use it, and have always had a compact too. My main interests are travel and history, and I can't be bothered with the bulk/weight and possible security issues associated with a DSLR, which I don't need for this type of photography. Others feel very differently, but I find a compact fine for 'supporting photography'.
We have a TZ9 which is an earlier incarnation of your TZ18. It's still a bit bulky for a 'pocket' camera and I would have preferred the Canon S95, but my wife wanted the telephoto capability, and she was paying for it! It's a decent camera, but nothing special IMHO, and I actually prefer my old Canon A640, although it's not a pocket camera either. I just seem to get better results from it, although I'll admit that I haven't spent nearly as much time with the Panasonic.