Meta Description Length Affects SEO Results
A long meta description is a sure way of diluting a site's search engine results.
The meta description is a slice of HTML code that is placed within the <head></head> section of a Web page. It usually goes in the document after the <title></title> tags and before the meta keywords tag.
A generic meta description tag looks like this:
<META NAME="Description" CONTENT="The page description goes here.">
Although it is possible to write a meta description that is 255 characters, it is a simple fact that search engines won't display more than about 155 characters including spaces.
Go to Google, Yahoo! and Bing and do a test search. Scroll down the page and look at each description. The descriptions come from one of two sources -- either the meta description tag or, if the page doesn't have a meta description, a snippet of content from the page.
For pages with meta descriptions longer than about 155 characters, the search engines cut off the display of the description with an ellipses (...).
The reason why a long meta description can impact search engine results is not so much the ranking of the page in the search engine as the likelihood of the searcher clicking or not clicking on the link.
If an important part of the description lies beyond character number 155, the searcher won't see it and will be less likely to click on that link and more likely to click on another.
So it benefits a site to keep meta descriptions shorter than 155 characters.