I will try to explain it as best as I could. I work a lot in 3D and to me, personally, there are two modes.
1. The "Working" mode where the Shadows are turned off and the Grids and the Axes are still visible. The visible Axes and the Grids help in modeling the lines more efficiently. However, when I am done creating my 3D Model and I have no changes left to make and need to present it to a client, I would turn on the Shadows.
2. The "Presentation" mode where there are no modeling changes but rather used just for Visualization. This, I feel is more useful when presenting the models to Clients as it is more appealing to the Viewer.
Of course, it is very easy to access the parameter from the Ribbon Bar. But, when I want to switch between the "Working" mode and the "Presentation" mode where the parameters are not just turning on the shadows, but also maybe setting the Background color, Kamera Animation Settings etc., then I think this would be a very good addition. However, I can totally understand it if there is not enough weight to actually implement it. Maybe not now, but in the future? I hope this gave you an understanding of why I think it would be nice to have a method call for turning the shadows to ON or OFF. Thank you for your time. Have a wonderful day.