The Erased component contains linework in the elevation object that you do not want to see. For example, if you have an elevation of a window front with three windows, but you want to display only one (for a higher level of abstraction), edit the linework of the elevation and assign the linework of the remaining two windows to the Erased component. Because the Erased component is turned off by default, the two windows do not display.
The hidden component is specific to 2D elevations, and cannot be defined by a material component.