Hey zahrindsilva
If you click on the "Setting" dropdown and select "Edit...", you can see what settings changes with each rendering quality setting, and even create your own custom setup for your renders.
The differences from the higher rendering qualities ("High" and "Best") mostly pertain to shadows, lighting and reflections and these will mostly be visible in renderings which utilize reflective materials, glass, water or high detail items which needs to cast shadows (like trees).
For most renderings using the highest quality will - as you have noticed - yield hardly visible differences from the lower quality renderings.
The "Screen/Printer" setting pertains to the resolution of the render - and this is where you will see really big differences if you need to use your render in large printed drawings/posters:
"Screen" will select a resolution which pertains to the actual size (in pixels) of the 3D-view you are seeing in Revit. If you scale the 3D-view you will notice that the resolution Width and Height will change accordingly.
"Printer" allows you to render in a much larger scale than what your screen can display and should only be used if you really need a high quality render for printing (even in standard sizes like A3, you will find that the "Screen" resolution will be enough).
For a better understanding on "Printer" and "DPI" vs. a normal render, you can read this article which i think explains it very well:
https://www.vsellis.com/understanding-dpi-resolution-and-print-vs-web-images/
