When you put a regular hole in a slab, the hole edge material is the same as the slab outer edge. This is a problem, since the slab can't clean up to walls of different materials. Using SEOs instead makes it possible to have a different material at a hole. The key is the option for new surfaces of target to 'inherit attributes of operator.'
Before SEOs, you would have to choose between this...
Slab edge has exterior wall material
...and this...
Slab edge has interior wall material
1. Place a slab where the hole should be, with the same elevation and thickness as the floor. Tip: Option+click on the slab, then change the pens to 10 and the layer to 'xRef Solid Cutting .HIDE'. Change the material to the material of the interior walls.
2. Get the two slabs in the 3D window. Tip: Find & Select for slabs of that elevation and thickness.
Floor & hole slabs
3. Do the SEO. Target: Floor slab. Operators: Hole slab. Operation: Subtract. New surfaces (the key): 'Inherit attributes of operator'.
After subtraction
Instead of choosing the lesser of two bads, we get...
Result
Of course, you could cut as many holes as you want, each with a different material.