Speeds up your website by making sure the gravatars are stored on your website and not loading from the gravatar server.
There's one problem with Gravatars. They are very slow to load. Each page with comments on them makes one call per comment to the Gravatar server. While a single call takes only a 100ms, on a page with hundreds of comments, we are talking about major slowdowns. Page loads can take 20 seconds and more.
This plugin solves this problem by:
caching gravatars with WordPress cron job..
caching gravatars on comment submission
maintaining a single copy of the default gravatar instead of downloading it again and again for all the email addresses with no gravatar associtated