WordPress by itself stores the name, email and url of the commenters into cookies (comment_author_).
This has the advantage that WordPress will remember your frequent commenters information and always have it completed when they return to your blog, without your visitors having to register.
Unfortunately this also breaks most caching mechanisms (Varnish, Caching Plugins etc.) in that the server will have to receive the comment_author_ cookies in order to properly autocomplete the information.
One way to fix this is to have the server (or your caching plugin/server) automatically discard those kind of cookies, but this will bring down the engagement of your visitors (they will comment less if they have to complete their name, email and url every visit).
The other way, is by using this plugin.
This plugin will move those cookies into the browser’s localStorage function, which will still autocomplete the comment form, but it will never reach the actual server, allowing most caching solutions to work without issues.
This is a plug-and-play plugin. No option required. No settings needed. You just set it and forget it.
It’s lite enough that it won’t impact your server at all – almost all the code runs on the visitors browser (client side)!