A back link and reciprocal link are identical. They both say the same thing to the Google engine, that your site should be ranked higher in the order because other people find value in what your website has to offer, thus they provide a link to your site. In turn, you keep a closed loop by reciprocating the favor to the other website by extending the same courtesy of a back link. Thus creating a solid network connection. Google likes to see interconnectivity and will reward your website well for planning it this way.
There are drawbacks to the equation. As things change a website that you are affiliated with may drop a hyperlink or a page may get accidentally deleted. When the Google robot goes through your website and finds a dead link it notes that you aren’t keeping good care of your website and punishes your web rank by reducing its point value. If you wish to know what your sites current point value is download The Google Toolbar and search for your website http://www.yourwebsitename.com in the box and perform a Google web search. Upon reading the full URL, Google will go directly to your site first thus pulling up your home page. There on the toolbar will be a page rank for your website between 1 and 10. 1 being a less visited and noted website and 10 a site that screams traffic 24/7.
Some of the individuals you share reciprocal links with may in fact scan all their links for continuity, should they receive a bounce back for a broken link on your website you can be assured you will receive an email from them. Keeping your website in balance with other sites you share links with will keep the Google engine happy. If you go off and add a company that is not Google friendly, meaning they have no back links you may also lose points.