The “Intens” wheel allows to set the brightness of the display. In a real oscilloscope this wheel sets the intensity of the electronic beam (this is the reason for it is called “intens” and not “brightness”).
If the same image is drawn on a real oscilloscope over and over again, the chemical substances used on the screen to make it shine get used-up sooner at those locations the beam moves across compared to other locations. Therefor intensity of the beam should be turned down on measurement breaks. On measurements the intensity should only be turned up just high enough to get a well visible curve. This will protect the display surface.