Remember that no one but Google knows why. This is why you try it and test to see what effects it has.
No one but Google knows. Any "SEO expert" that tells you otherwise is not telling you the truth. They can guess but they can't know.
I'm building links, not for SEO but to try and generate direct traffic, if these links are no-follow am i safe from getting any Google penalties? Asked another way, can no-follow links hurt my site?