The spin center defines the center point for the model when you rotate or move it in the graphics window. It is like a pivot point of the 3D model. This option just helps when viewing the models or assemblies and has got noting to do with the part features and other functions. A simple click on the spin center icon toggles the option on and off.
Spin center icon. (Normally located in the main menu
In this example, I have taken a simple square block with a small hole at a corner. You can see the spin center at the center of the model in the video below. In the video, see what happens when you on/off the spin center. Here is the best option. If you want to see the whole part or assembly, switch on the spin center. If you want to see a specific feature in part or a specific component in an assembly, switch off the spin center.
Spin center on - The pivot point for model graphics rotation is the geometry center. Spin center off - The pivot point for model graphics rotation is the point where you press the middle button to rotate the view. See the video to understand that.
That's all for this topic. I hope this helped you.