Write ES5 and time how long it takes you to complete projects of a given size.
Write reactjs code but use the JSXTransformer. Watch page performance. Watch how many times you reload the page in a given sitting.
It's really only when you find yourself with a problem that you can quantify that these tools start to make sense.
Discover for yourself why these tools exist or you'll waste a ton of time learning the newest thing and in the end not have gained much at all.