I saw the need when I had a couple of simple apps where I didn't really have a web server where I could create payments/subscriptions via stripe's server-side libraries. I also didn't want to use stripe's Checkout. I had to spin up a simple service just to confirm the payments and I figured I could abstract it.

The signed jwt response can be helpful because now you just need paysly on the frontend and your backend can be dependency free - all it needs to do is parse the token.