Control which image is used when people retweet your URLs.
In order to make sure that images of your domain are displayed correctly on Facebook and Twitter social networks have published guidelines on how to set a preview image. This allows every user to get a good preview of your site in social networks.
If you or someone else shares your website in a social network you want other users to get interested enough to follow the link to your website. A preview image is more likely to be clicked than just a title and description. And don't just use any image of your website as a preview image – pick the image that will interest people the most!
Here are further resources on the topic: