Many listing or directory services ask company owners to add a link back to them. The primary purpose of this of course is for them to promote their company.
Generally we don't recommend linking out to these services unless they add some credibility or trust factor to your company.
For example, a link to a BBB certification can build trust in your company, so that could be very valuable on your website.
The key question to ask is: Is the information I'm linking to important enough that I'm willing to direct my visitor away from my website to see it?