Meta descriptions tags generally worthwhile, when you’ve got nothing better to spend time on.
The main value in them is to boost the click through rate (CTR) from search results to your site — they can be effective in doing this if you craft them well.
Meta descriptions can also be used as a branding tool to get certain messages into search results for people to see even if they don’t choose click through.
They can also assist with legal compliance issues, such as placing disclaimers in close proximity to any controversial text in your page title tags.
Meta descriptions are thought to also have a small influence on rankings, but CTR is still the main purpose for them, and CTR has a direct, significant impact on ranking, but that can be a positive or negative effect, and for this reason some SEO experts leave them alone, especially on large sites and busy pages where it can be a huge maintenance task to ensure these descriptions don’t become out-of-date in which case their potential negative influence becomes a serious threat.