Hello Hurt,
I cant really go into detail on how much better a material instance is, but the advantage of instances is that they can share unaltered calculations.
Besides that, workflow wise its easier to just replace a texture in an instance, instead of having to set up the material again. and in the case you eventually want to add a small variable value tweak, you instantly have it among all other instances.
I personally would go for a master material + instance workflow whenever possible 