The value or worth of a link will vary from person to person, but the main objective of any link is to bring traffic back to your website. Traffic - the ultimate goal of any link is to generate traffic. Obviously, the more traffic a link can generate the better the link is. Type of traffic - If you can receive targeted or relevant traffic it is much more valuable than non-targeted traffic. Link Location - It is important that the link is easily accessed. If the link is located on a page that can only be accessed by clicking through 5 other pages the link isn't worth much. Also, if the link is coming from a "bad neighborhood" on the internet that will decrease the link's value. Link Type - Is the link a one-way link or reciprocal link. A one-way link is much more valuable than a reciprocal link especially to search engines.
a link can have value even if it doesn't send you any traffic directly. It can raise your ranking in the eyes of the search engines.