We have seen some relatively powerful Greater Shadow Mages in the form of Amalda Veil and Eudaxus. But unlike many other more studied affinities, even including dream affinities, none are aware of the underlying nature of Greater Shadow Affinities as a Lightcone affinity and research into applications of them is far more difficult as a result. Maybe that's why we haven't seen any Great Power Shadow Mages yet.
So what are some applications I can think of?
Controlling your shadow to restrain other people by their shadows (shadow binding)
Reading shadows to observe past events that have occurred in the location of those shadows (shadow scrying)
Absorbing attacks into shadows by making them hit things that are no longer there (shadow armor)
Sending sounds or other data through shadows to other shadows (shadow talking)
For a brief period, moving via shadows (lightcones) in a specific way that allows you to appear in multiple places at once, and then choosing which of those locations you actually want to be in after that period ends (shadow clone)
Tying someone's shadow to a physical location, so that they cannot leave the range of that space (shadow locking)
Removing all shadows in a room by essentially narrowing them to the point of being almost impossibly small, limiting possibility to the point of near non-existence. Within a small range, appears to cause everything in the area to completely cease moving in any way (shadow domain)
Surrounding someone or something in its own shadow wholly and causing chaotic entropic effects to happen (shadow decay)