I like clutter... to a point. Things on shelves, plants in corners or on tables, rugs and paintings make a place feel more real for me. Everything has to be functional, though. If you can't sit somewhere because something is placed too close to something else, there's no point. I also don't understand the completely amazing, fabulous-looking builds where "stairs" are made out of shelves and there are fake lofts a Sim could never get to. Are they used for photos?
Anyway, I like clutter, but I resist over-doing it for builds I upload and play-testing is a must.