Tools like Fillet and Insert Polygon Edge are great for working with 2D and 3D Polygons. But they have other uses as well that might not be so obvious.
During the design process lots of things can change. Maybe you add or remove a porch. Or perhaps you add or remove a room. But that doesn't mean you have to throw away portions of your previous work and start over.
Removing Edges With Fillet:
The Fillet tool is useful for joining the ends of two lines or walls or for removing parts of a Polygon.
Select Tools-->Fillet and select two edges. This allows you to remove edges of a polygon.
Now let's look at a roof. You might not have realized that Roofs, Floor Systems, Areas, Ceilings, Interiors, and other items are Polygons too.
Suppose you have something like this configuration but then later decide that you want to put a covered porch in this area. No need to erase the roof and start over. Use the Fillet tool. Select Tools-->Fillet and then click on the two edges of the roof that you want to join.
After using the Fillet tool the roof edges are removed.
Adding Edges With Insert Polygon Edges:
You can use the Insert Polygon Edges tool to add edges to a polygon. In this image I started with a rectangular polygon and then used Insert Polygon Edges to add the cut-out on the upper left.
You can use Insert Polygon Edges on any polygon including Roofs, Areas, Floor Systems, Ceilings, etc. So we could have removed the covered porch from our previous Roof example using Insert Polygon Edges rather than having to redraw the roof.
Note that when using Insert Polygon Edges it often becomes necessary to adjust the edge lollipops to get them to reference the wall.
Also, in Roof Mode there is an equivalent tool called Insert Roof Edge. This is the same tool as Insert Polygon Edges. It just has a different name and is included in the roof tools between Add False Dormer and Add Shed Roof.