Right now (alright I am only looking at R19) when your 3d view has a section box applied, you can only move its boundaries by eye-balling them. This is hard to do if you work your way through say voids in a floor because there may be no land marks to eye-ball by. The idea is to have the same number input that revit would provide when inserting a wall or pipe. Negative numbers could go the opposite direction the mouse is heading in.