In all the cascading shadow map explanations I have read, the final projection into the shadow-map is done using an orthographic projection. This makes sense for a directional light because a directional light "sees" things orthographically.
Spot lights on the other hand "see" things with a perspective transformation. Once we have our light space bounding volume, should we be performing the final projection into the shadow-map using the spotlight's projection matrix, rather than an orthographic projection matrix?
Perhaps I am missing the point here. Cascading shadow maps are necessary to provide shadow maps over large areas, thus because spotlights tend to have a very limited area of effect, perhaps cascading shadow maps are not necessary for spotlights.