As a thing, OS development requires some UI to interact with low level things, .. And for me most satisfying - put reward aside , as I'm not interested in material part -, thing is Game Development, tools to see parts - debug lights bounce with a terminal - of render process ( Some may check Unreal Engine, or any other game engine UI's ), Even I don't fill comfortable enough with blueprint kind of low level UI's as oppose to text programming ( double d = 10.0 is easy for me to drag and drop a variable ) Material always have many faces. UI is one of them.