Titles and meta descriptions are important for good listings in the search engines.
A title that matches what the user has searched for will get a boost in the search results, but the title must be factual and a fair description of what was on the page.
The description is not so influential but will normally appear in the search results if supplied. This gives you a chance to influence the user while they are looking at the search results. If you don't have a description the search engine will pick a fragment of text that includes the key phrase the user searched for, or at least some of the key words. This fragment may not be your ideal choice, so it's better to use a meta description you have devised yourself.
The search engine will embolden words in the description that match the user's search terms. If you use more key words in the description then more word will be in bold, and the more relevant your page will appear to the user who is doing the searching.
Lengths for Search Engines
Search engines use the title tag when listing pages in the search results but will cut off long titles after a certain number of characters. This length is not the same for all search engines and not always the same for the same search engine. Recent experiments gave these maximum lengths:
Restrict your title to 61 characters and your meta description to 156 characters if you don't want the search engines to cut them short:
<title>This Title Tag is Exactly 61 (sixty-one) Characters in Length</title> <meta name="description" content="This description is exactly 156 characters and two sentences long. Words here that were in the user's search term will be highlighted in the search results." />
If you are creating your description programmatically from the page content, take the last word boundary before 157 characters, not counting HTML tags. Don't repeat the title.
What about the "keywords" meta tag?
In days of old, search engines used the keywords meta tag to help decide if a page was relevant, but webmasters started "stuffing" the keywords tag with words that they though would help them get better search results. So the search engines gave less attention to this tag and even penalized sites that appeared to be trying to cheat the search engines by using irrelevant keywords. Key words in your title, meta description, as well as scattered through your page content are much more important if you want to move up the search results.