how do you furnish a mansion?

I've run into that issue, aside from using the decorative items here and there it sometimes good to keep some open space and also add things one might not consider a family home. Like a room specifically for parties where you quickly add sims to groups make them go to the party room and lock them in so they aren't just isolating themselves on the computer. Which I don't personally mind but for pics good when they are just in one room. A separate office for both parents in case one works outside the house and the other works at home, a lounge area on the other side of the house than the living room. Playrooms for kids or pets if you have C/D. It's the little things that fill up a mansion a little easier. :)