Most WordPress themes show user Gravatars in the comment threads. It's a way of showing an image with the user, as associated by the email address used. It's a nice touch, and almost an expected design pattern these days.
Every one of those gravatars is an individual HTTP request though, like any other image. A comment thread with 50 comments means 50 HTTP requests, and they aren't always particularly tiny files. Yeesh.
Let's lazy load them.