I wanted to use an example from the real world of what happens if you don't give your pages a meta description. As you can see this example is from the Smart Passive Income - Get Started page. I did make Pat Flynn, owner of SPI and this months must-read book author, aware of this in August 2014.
This is the end result in a Google Search Results Page
As you can see the end result is a bit of a mess and unlikely to help you gain clicks from users who find the page in search. Below the main result you can see how Pat normally completes his meta descriptions.
If you are writing your Meta Descriptions here are my top tips for creating a killer meta description.
Update 23/9: Within hours of posting this article Pat updated his site, and as he said it kicked his butt to do it. It literally took him a few seconds to do I would think, and he will probably reap the rewards.
@andykinsey Kicked my butt to make the update just now ;) Thanks!
— Pat Flynn (@PatFlynn) September 22, 2014
And this is how it now looks, less than 24 hours later, in a Google search. Much nicer.