This line only appears on the dialog box when you use the last tool.
The Max Step Height is the actual height of the rough cut steps when the first tool is used. If you change the Max Step Height for the first tool, the actual height of the steps is the new value.
The Step Reduction Step Height for the previous tool is the actual depth of the rough steps made by the current tool.
If you change the Max Step Height for a tool, the previous tool Step Reduction Step Height can change.