It likely to be true for any "property," e.g., for physical strengths, it not great to be weak, say below 5, it's pretty great to be string, 7-8, but super strong, 9+ takes inproportional amount of effort and is simply not worth it. Same goes for apartment cleaning, I like the 7-8 area, but would not really want to do or even live in the sterile 9+.