Is there a way to subdivide a face without using ctrl r and creating unnecessary polygons? Blender beginner here, I want to add some stairs to the front of my model and my initial thought was to subdivide the currently flat staircase face and then translate every second edge running down the face so that it forms a staircase. However the only way I know of doing this is to use ctrl r and loop cut the entire model which would create numerous unnecessary polygons on the rest of the model. My question is: Is there an alternative way for doing this which doesn't create so many polygons, while keeping all of the stairs evenly spaced? Thanks in advance for any help!
Yes you can, by creating "n-gons". Bad for topology, usually but it can be done like this:

in edit mode select just the side edges of the slope then subdivide them enough (use edge tools > subdivide - CTRLE): 



you get edges subdivided as you want along their length. Now activate vertex snapping, and in side mode select vertices like this



then (with all those vertices selected) grab them along global Z and snap to their bottom unselected vertices



then do the same but on global Y with their upper unselected vertices



you get this in the end:



of course this is just a simple example...