You are not showing a graph of usage. You are showing a graph of clocks and voltage. My guess is you are using applications with hardware acceleration, which will cause your GPU to increase its clock rates while being used to help accelerate what ever the software is doing. Logitech gaming software does this, most browsers do this, flash does it, and a number of other applications use hardware acceleration. The GPU "usage" is still likely low, but the clocks will increase while using these applications. Most these applications do have settings that allow you to turn off hardware acceleration, but are usually set to be on by default.