Meta description is not important for ranking. It sometimes appears in search results as a page description (but not always) BUT it doesn't have any impact on page position in these search results. It was sad officialy in few places. It's for a cup of months already. This meta (and keywords meta also) was overused or used in a wrong way. There were even pages with keywords and description related to one topic and with content related to totaly different topic. The most important for page position is the content. You can have valuable content for some search phrases and your page may high in searc results, and if you have some 'strange' meta description, not related to the content, google will use first paragraph of the content in search results if google descide that it is better for users to show as a page description.
But it doesn't mean that meta description is not important at all. It is important, but not for page position in search results. You should use this meta and it should be unique on each subpage and strictly related to subpage's content. If your subpage appears in search results and meta descripton is related to subpage's content this description will be visible to users in search results, and the can make some decisions based on this description.