I used WordPress to setup a website. I want use excerpts as Meta descriptions. Is it necessary to do this?
Necessary? No. The meta description is not required by WordPress to function nor is it used by the search engines for ranking purposes. However, some search engines, including Google, do use it for possily displaying its content with a page's search result listing. This means it affords you some control over how your search engine results appear. Since this is easy to automate with a CMS like WordPress it is worth doing.
Adding to what John wrote, it's best to add good meta descriptions that use your keywords, which will be bolded in search engine results (i.e., the "snippet"), and entice search engine users to click on your link.
If you don't add your own meta description, the search engine will pick this for you based on the keyword searched on and string around it, as covered here
Using plugins that create automated descriptions will likely just result in the first line of your post to be used as the meta description, which might be less descriptive and effective than what the search engine will automatically do. So it's best to use those as a starting point and customize the resulting meta descriptions further to include your keyword(s) and to be more descriptive.
If you use the WordPress SEO plugin, you can visit the SEO > Titles & Metas admin menu, and on the Post Types tab, set the post template for meta descriptions to
This will mean that post excerpts (ie: custom excerpts written in the metabox and used on your site) are used for the meta description tag by default, but you can override this on a post-specific basis using the SEO meta box on the post editing screen.
Meta description is not necessary if you are happy about how your website looks on Google SERP.Use Rich Snippets tool in Google webmater tools to preview how your webpage looks on SERP.
Meta description used to display a summary of your webpage content on search results page in less than 170 characters.
Meta descriptions might not be required technically for your website to either function properly or rank better on a search engine, but they do have aesthetic value.
Meta tags are reflected on the search results page of various search engines. A well written title and description might attract a human to click on the link.
So in summary, meta tags like title and descriptions are still required though not mandatory.