An update on what? That’s the explanation
This does matter.
The assets of the site have to be downloaded. They benefit from caching, but if you return much later you may find there’s a chunk new to download.
That’s no different from having to update an app, but it happens automatically and every time. That’s the nature of web apps.
One of the significant benefits of this approach (similar to native apps) is that the incremental data retrieves whilst using the web app are much smaller since most of the client code is already loaded in the initial load and you are usually only downloading relatively svelte json data as you navigate and do things.