To me it doesn't make sense to assign lot challenges just based on world. Some things are annoying enough not to want them in my game on every lot. I do enjoy the simple living challenge and I think I now use it on most of my lots, if not all. For everything else, I just assign them based on what the lot is intended for, it's surroundings and it's owners, sometimes it helps with their traits, sometimes not, and some lot traits that help with skill building I use only on community lots to encourage my sims to get out of their houses.
