You don't have to use all of them but if you really want to enjoy the full watch experience it's highly recommendet.
If you want no Ads obviously
To skip in Video Segments like "Reminder to Like"
Uses the data from youtube before they removed the dislikes and than counts the dislikes from every other user of this extension.
This has every feature you can possibly think of and may be a bit overkill for the average YouTube enjoyer.