Metatags are essential in web pages. This give the searcher a quick overview, in 1-2 sentences about what that site or page is about. When a searcher has typed in a search term, google will give out the results. You will see the title tag, Which is the large blue text on each result and below it, a quick description about what the page is about. Usually, a meta tag, is placed in the code of the web page giving a description of the page. If there is not one, google will try to take a snippet from the page which it thinks the page is about. Now google is quite clever in obtaining this information, but I would personally like to put in my own description, as should anyone who has a web page, to explain what their site or page is about.
As you can see from the above image, I searched using the keyword, landscaping and the top 3 results are above. The meta tags are in black text with the keyword bolded making it stand out. Ensuring a keyword you are targeting is both in the title tag and meta tag is important if you want to catch the searcher's eye, and have google rank that page in the search results for the keyword you are targeting.