Meta descriptions were once considered as an important ranking factor and all the SEOs and web masters took care in creating keyword enriched meta tags for better rankings. But later major search engines such as Google and Yahoo have openly stated that meta descriptions are no longer given importance as far as search engine ranking is considered.
Even though Meta descriptions are of not much importance in the ranking algorithm of Google, it is useful in some other ways. Meta descriptions are shown in some of the search snippets and a well written Meta descriptions can enhance the user experience and thereby increase the click through rate. Since meta description is no more a ranking factor, it is always better to make it as creative as possible for better traffic conversion.
If a web page has enough content, then Google will automatically pick relevant snippets from the content for a particular search query. So for a web page with rich content, Google would go for the snippets from the content rather than from the meta description. In this case the web page will perform well even if there are no meta descriptions.
But in the case of a web page with minimal content is always advisable to create a well written meta description for better conversion. In the case of minimal content, Google will be showing snippets from the Meta description and hence the presence of Meta description in mandatory. The length of the meta descriptions should be limited since different search engines shows different character length from the meta descriptions. For example Google displays up to 160 characters and Yahoo displays up to 165 characters. So the length should be kept in mind while creating the meta description for your website.
The introduction of personalized search results by Google has increased the importance of a compelling and well written meta descriptions. As told above a good written meta descriptions can help in increasing the click through rate (CTR) and an increased CTR plays an important role in increasing the search engine ranking for that particular keyword. So if a particular keyword is being searched by a searcher, and if he is forced to click on your website which is ranking lower in the results only due to the compelling meta description snippets, it would definitely improve your keyword rankings.
So those who consider that meta descriptions are outdated, it is high time for you to rethink on your opinion. Try to create a well written, unique, compelling and well optimized meta description for better CTR and better search engine rankings.