I usually redo the entire world I want to play in before I place any Sims but it's slow going, right down to the rocks in World Editor, lol. Sometimes I need a break so I might start a new game with a new Sim in a different world and alternate between the two. For me redoing a world takes months. Sometimes I can redo (building changes) or redecorate an entire house in a day but not often. I often get the whole house done then don't like the color and change everything, which is easy thanks to Create-a-Style. I can try out several different color schemes before I find "the one" for my sim.