Most of the time I’ve used Substance Painter only to paint Material ID colors quickly; it allows for easy UV Shells selection and let us paint these UV shells directly on the 3D mesh, that is awesome.
But, Quixel has lots of premade effects and I love its many edge detection filters; so I take the Material ID texture painted in Subs.Painter and go with Quixel from most of the time.
Subs.Designer requires knowledge of graphics programming and GPU architecture to work well there, and I suck at graphics programming 
For me it is only useful if material needs configurable destruction layers, snowy terrain, weather variations, damaged walls. That kind of stuff.