What it does
Happy environment moodlets like 'decorated', 'nicely decorated', and 'cheerful decor' will never be given to sims. Moodlets from emotional aura objects are not affected, because those can already be disabled in-game if you don't want their effects.
Why would you want this?
The whole environment/decoration thing feels like its importance got broken along the way from Sims 2 to Sims 4.
In Sims 2, environment worked like a need bar - it had equal importance on a sims’ mood to their bladder or fun levels.
In Sims 3, its importance got downgraded from a need bar to just a moodlet.
In Sims 4, it’s implemented similarly to Sims 3, except moodlets are now far more powerful than needs bars at positively affecting mood, which has sent it all out of whack. Needs bars no longer directly affect mood, and it takes getting all your needs bars to full to get +1 happy. Whereas environment gives you +1 to +3 happy all the time.
When people complain about sims being overly happy in The Sims 4, I think a good portion of the blame for that can be attributed to the 'nicely decorated' happy moodlets. If you have a room that’s made to look like someone lives there rather than being a sterile plain box, you’re likely to end up with +1 to +3 of permanent happiness added to all your sims, whether you wanted that or not.
Take those moodlets away, and the balance between positive and negative emotions gets more interesting, I feel.
