I like to play unrated because it is just for fun - I'll offer to play 5 0 with anybody rated between 1 and 2500.
I play blitz to relax, and when I play rated I tend to have too much anxiety over the rating points.
I have had a very few players insult me and say that my rating is way too high, etc. but who cares.
What's your theory on when to play rated vs unrated games? Personally, some days I know my concentration is subpar, so I choose unrated. Other days, I just feel like playing lots of chess, but I only have a limited number of good games in me, so I switch to unrated. What about you?