I have to admit it: a nice compliment brightens up my day!
Out of the blue somebody - a friend, a colleague or a complete stranger - makes a positive remark about what I wear, how I look or act. When it's about my appearance that might sound superficial, but my surface is a part of me. I might have put a little effort in combining colors and in looking "neat and tidy" and it simply makes me happy that others appreciate that effort :-)
I also like giving compliment, assuming that the other person enjoys being seen. Yes, basically it all comes down to that: the pleasure of really seeing others and the pleasure of being seen ourselves.