In the ViewModelEditor the property "Act As For Actions" helps you in the following ways:

If you have a grid with objects of type B - but many of the actions you want to expose on these objects reside on class A then you enter an expression in the "Act As For Actions" that navigate from type B to type A (expression must end up in 1 or 0 objects). This would save you the trouble of creating new class actions on B that repeat the logic for the class actions on A.

This scenario is common for association objects (multi link between A and C with a link class B in between) - you want to precision offered by B in the grid - but you want the actions of A to be available also. In this case the context is B and the expression would be self.A.