Activating Twitter Cards will cause the plugin to output certain meta tags in the head section of your site’s HTML. Twitter cards are pretty much exactly like Open Graph meta tags, except that there is only one network, Twitter, that looks at them.
These will allow tweets of your content to contain images and descriptions. This will make the tweet far more visually enticing when folks on Twitter see them.
Pro Tip: Check out our advanced guide, Open Graph Tags and Twitter Cards.