You can see the dust, and eventually you will feel the need to do something about it. Oh everyone pretends they clear out their case every couple of weeks to maximise efficiency but they know it's secretly a chore.
Also, if you leave your PC on overnight for any reason, you'll have the light of a thousand suns obnoxiously illuminating every crevice in the room. You will have neon dreams.
And, you cant really soundproof a window. Your menagerie of 80mm fans will drown out the silence in your life.