Meta descriptions are extremely important to SEO. But writing unique meta descriptions for every page of your site can be a time consuming and daunting task.
Crafting meta descriptions page by page doesn’t necessarily scale well for large sites.
For each page, you must identify a keyword and carefully craft an enticing message that clearly identifies the page content, includes the keyword, encourages clicks and is less than 320 characters.
Form most sites, this is difficult. For large sites, nearly impossible.
When sites exceed hundreds or even thousands of pages, meta description quality can suffer. It’s tempting to use automated systems or templates.
While templating isn’t going to create a great description, it’s at least better than allowing Google to simply display the first 300 characters of page.
For more on automated and semi-automated meta descriptions as well as pros and cons, read “Reducing the time it takes to write meta descriptions for large websites” from Search Engine Land.