Meta tag descriptions have long played a significant role in the optimization of websites for search engine placement.
A great deal of attention has been paid to the tactic over the years, and discussions about optimal length, and the density of keywords and phrases, are routine. One of the more common questions however is whether every page of a website needs to have a unique meta description.
Google's Matt Cutts recently suggested (in the video below) that there are really only two viable options - either have unique meta tag descriptions on each page or don't use meta tag descriptions at all. Above all else however, make sure that you don't have duplicate meta tag descriptions. That's, fortunately, an easy fix as Google's own Webmaster Tools crawls websites and provides notifications if duplicate meta tag descriptions exist.
Google has been known to auto-generate descriptions of pages (primarily for the search results page) when no description exists. Cutts suggests that webmasters and search engine optimization professionals develop unique descriptions for their most important pages (home pages, high converting pages) as well as those when the auto-generated description isn't very good or appealing to users.