Let’s face it, Gravatar should have been a plugin from the start, but Automattic chose to shove it down our throat from the very start in 2007. If you use WordPress as a blog, you may want to keep it to get the commenters’ profile picture in a simple way, if you use WordPress as a CMS or don’t allow comment, you have no use for gravatars.
Gravatar’s impact on speed and space usage a your WordPress site is not negligeable. Every single comment that includes a Gravatar requires a separate call to the Gravatar servers, which means about 100ms spent per call. If you have many comments, make the calculation for yourself.
In terms of storage space, Gravatar images can take some substantial space if you have a large WordPress site. However, space usually isn’t an issue for most websites.
If you want to keep Gravatar, you can mitigate the issues caused by its usage, you can employ strategies such as caching Gravatar images to reduce HTTP requests or use a Content Delivery Network (CDN) to speed up image delivery.
Removing Gravatars from your WordPress site is extremely straightforward and simple. In your WordPress admin, just navigate to Settings > Discussion, then scroll down this admin page until you see the “Avatars” section. There, uncheck the “Show Avatars” checkbox.
If you dislike Gravatars, but still want to use avatars on your website, the easiest way to do it is to use the WordPress plugin Simple Local Avatars. Installing this plugin on your website will allow you to turn off Gravatars and replace this function with local avatars. It also gives you useful customization options to decide who can upload his/her own avatar and the avatar image size, among other things.