Meta titles (The ideal length is between 156 and 250 characters) are an important factor for humans and Search Engines so they should, ideally be keyword optimised to the fullest extent. Meta descriptions have a significant influence on user click-through rates from the SERP as it is a great opportunity to entice the user through creative and descriptive text. Meta titles should be well-written, and keyword optimised. Although meta-data does not directly impact ranking, CTR does and the better your meta-data, the higher the CTR. Unlike other search engines, Google does not religiously show the Meta title in the SERP if it feels there is a more appropriate match with text elsewhere on the page. If this is a common occurrence, then review your Meta title procedures.