I assume one is the default/state of the parent material (instance), the other (the right one) is the setting of the material instance I am looking at… But what effect does it have is one is set and the other not?
Any short description or link to a good tutorial / documentation would be much appreciated.
this works exactly the same as #ClockWorkOcean explains. you can understand the left check box as a reset button. if it is on it use your given value and if it is off it uses its default value given in its parent.