Projection Ex is a system to work around the limits of the native projection nodes system in LightWave 3D.
Some speciality projections such as Triplanar require more than one texture sample in places, which implies that they also require more than one UV coordinate per surface spot. The native projections don't allow for that, which is why Projection Ex has been created.
This allows for cleaner node graphs with nodes dedicated to a specific function. One example would be creating a Triplanar Projection Ex, adding Repetition Projection Ex to it and using the resulting projection to drive all images used by a single PBR Texture Set.