David Kimura PRO said about 2 years ago on The Stimulus 2.0 Tutorial :
  I believe the main benefits of Stimulus is isolation, reloading, minimization, and ease of use.

Isolation - The controllers don't leak over into other pages. If the data attributes are present for that controller, it will work, but is deconstructed after the page refreshes or navigates away where those data attributes are no longer present. This makes working with complex front ends really nice. There is a caveat though with something like getusermedia where the use of a webcam or audio source could leak from one page to another and must be handled properly.

Reloading - Whether you're loading the controller on a new page refresh, adding in controllers via UJS, or even rending a partial sent over websockets, the controller will initialize and work. This use to be a pain in situations where UJS wouldn't initialize a datepicker and you had to manually initialize it again.

Minimization - You get a lot of functionality from such a tiny library. Even then, you don't have to write a bunch of Javascript to get highly interactive front ends. This combined with Turbolinks/Turbo makes for a super powerful tool.

Ease of Use - By following the conventions, you can make your javascript more readable and easier to maintain. Write less javascript and get more functionality. Bringing in additional libraries is easy with webpacker. This will be interesting to see how things change if we revert back to sprockets, but for now, webpacker is a very viable solution.

I recommend that you check out some of the other videos like Google Maps API,  Video Chat with WebRTC, FullCalendar, AutoComplete, Drag and Drop, Audio Recording, QR Codes and Cropping images. All of these are accomplished using StimulusJS.