SeenThat is a chrome extension that hides YouTube video recommendations depending on how much of that video has already watched. It functions like any other extension in that that runs this functionality in the background while the user browses the web. What gets hidden can be easily customized by clicking the extension icon on the chrome toolbar and changing the settings in the corresponding popup window. These range from toggling which YouTube pages SeenThat will be active in, to details regarding the types of recommendations and the minimum percentage watched to hide.
Before SeenThat could be published, the extension had to be submitted to Google for review. This serves to both ensure items added to the Chrome Web Store aren't malicious and to make sure that extensions only use as many permissions as necessary. This holds true for any updates to extensions, meaning that there will be a delay before new features and bug fixes will be available to users.
If you're sick of being recommended videos that you've already watched, you can find the extension from the Chrome Web Store and install it by clicking "add to chrome".