Well, I've been writing web apps for a living for the past 20 years or so, and I've written lots of full stack apps. There can be plenty of ephemeral state in a non-trivial UI. For example, I worked on a discharge summary app for a hospital at one time. The app had to aggregate data, such as patient demographics, medications, allergies, and so on from a bunch of different services. This data would need to be pulled gradually based on what the user was doing. All of the data that got pulled and entered by the user would represent the session state for the workflow. Maybe don't trivialize something you admit having no experience with.