Hello,
I don’t understand what’s the idea of attribute promote?
For example: if you are creating color attribute, you can choose in attribute create on which class it will run.
So when attribute promote is useful?

You can use attribute promote to move an existing point attribute to a polygon attribute, for instance.

Attribute promote can also be useful for promoting a max value of say a point or prim attribute to a detail and setting the method to maximum to be accessed somewhere else by using a detail function. The methods drop down menu is where alot of functionality comes in. That was just one example. You can also get the min value.