If you have tons of Swift code that needs to run in watchOS, iOS, iPadOS AND the cloud, this would kinda make sense... but how frequently is that the case? When I was still doing mobile the goal was to write as LITTLE client-side code as possible and put as much logic/heavy lifting on the API side as possible because we can make changes there far quicker than in the native client. And almost all of the client-side code was about GET/POSTing to the API or interacting with the SDK to draw things on the screen -- almost no business logic. That said, I didn't work much on apps that were supposed to work without a data connection for long periods of time... in that case it's more likely you'll run into scenarios where you're writing business logic in the app (in Swift/ObjC) but even then the goal was to keep that kind of code to a minimum (or less).