@eternalrainn for me, it is because I don't like seeing them there- hanging down from 'mid air' and getting in the way. I know they fade out when you zoom in, but I still don't like it.
And, you're right, some people do make rooms too bright. I have even downloaded lots where people have used MOO to overlay a few lights in the same spot.
I prefer more subtle lighting and will sometimes colour the occasional light to give an area of a room a different ambience. I do like my kitchens to be well lit, but even then I feel it only needs one saucer light (or 2 for a long kitchen).