Though Google picks meta description dynamically from your page but many a times despite the fact that you may have written its meta description but basis on your most searched keyword or target keyword, its good to write Meta Title and Description Tag specifically to the target keyword.
I myself have experienced the magic of having meta tags for some posts. Posts which has all the meta tags in place, rank faster than the post which doesn’t have. Though, it doesn’t mean that posts without meta tags do not rank higher, but still it advisable to have meta tags on your post.
Its all about Click Through Rate (CTR) – All it matters is CTR on SERP, more your website’s article gets clicked, higher the chances that it would gradually move up, it has also been proven by many of the search experts while experimenting ( a trick where group of people across a region deliberately clicks certain listing ranking in lower positions, and that listing comes higher in SERP eventually, though it remains for shorter period of time ) Therefore, it is always advisable to optimize for Clicks rather than Rankings and every time we can not trick Search Engines for result page manipulation but rather do it in a systematic manner by adding proper meta tags that could bring more clicks.
So, try adding meta tags to some of your new, old articles and Do share your comments or feedback on the same.