Looking at pictures of people I know -- professionals in accounting, law, financial advisory services, etc -- and seeing them stone faced leaves me cold. I can only imagine how someone who's never met them might feel.
It's a tough world out there. We all want to work with people who add a little brightness to our day.
Smiling, even a little, in your bio picture suggests you're a positive person who might be enjoyable to do business with.
If you think I'm nuts, consider babies and dogs. When you smile genuinely at them, babies light up...they beam back at you, gurgling and laughing. And (most) dogs will wag their tails and approach you. Guess what? Same thing happens with grown-ups!
Why not up your chances of business people approaching you, too, by exhibiting a nice, friendly smile.