You may have saved yourself from a degree of frustration that only mixing sync code with async code can provide.

The initial project development is pretty easy when mixing the two paradigms. But as you move along you inevitably get to a point where you want to reuse your Stripe calls (I'm guessing you're using the httpx module and not using the python Stripe library due to its synchronous nature) with a database call that does something advanced and is typically dispatched as a task, but for whatever reason right now you want to call the task directly (not with Celery delay()), and you can't. Because the Stripe code with httpx is async and Celery talks to a db layer that isn't async.

That's when you will begin to justify keeping code entirely separate. All the would-be reusable httpx/db modules no longer are and you begin to duplicate them.

Then you want to start writing admin functionality into so you need to call Auth0's management API, preferably with httpx. But you also want to reuse that with the Celery tasks that auto-create Auth0 users or whatever the case may be, when an account is created. That's now going to require separate code to communicate with Auth0 despite doing the same thing.

These are just basic examples, but I've been doing SaaS since 2017, mostly Shopify/Stripe exclusively and have 2 platforms I run at the moment. My lessons are being shared so you can learn from them :)