I'm developing my first game for mobile devices in Unity3D. My game uses a 720p-resolution. Currently the UI uses the same one. So far so good.

I heard that professional game-developers create their games in a way where the UI uses a much higher resolution than the game itself in order to deliver high-definition graphics for the UI-system.

So in my case does that mean I have to create a much higher resolution for the UI so it looks crisp and sharp even on large mobile-displays (e.g. tablets like the iPad Pro, etc.)? Is 1080p a good resolution for the UI I'm creating? Or shall I stick with 720p? If I use e.g. 1080p for the UI do I need to scale down the UI in Unity3D?