I don't understand why OSX needs to restart the app to grant it permissions. The most annoying is video chat apps such as Teams and Zoom, having to close everything and reconnect if you want to share the screen or such. Perhaps there's a technical reason but it just feels like a lazy implementation.

But about the unix permissions model, is it really useful? During all my years of using linux on my personal machine, I've always had everything owned by my own user. Setting up specific users for programs would be a pain, and I don't think anybody does that? Servers is a different question, because then you're not actively using the system in the same way, which makes managing user accounts and their permissions on an app-level doable.

For normal users I think what's done on iphones and such works fairly well, and there they actually seem to have implemented it properly so that it doesn't require a restart to grant permissions.