I am not 100%, but was told that this was used to make mass produced images. The dots, as my best guest, was used to even out the exposure. I am sure that someone on here has more experience with it and can weigh in better than me.
I must admit that it's a fascinating piece of gear. It was probably groundbreaking when it came out.
Here's the translated wikipedia page
The Agfa Variomat was an exposure frame for the photo laboratory. With it, the exposure of the photo paper in the positive process could be automated for the first time. For this purpose he had a built-in exposure meter in the housing. A complex circuit of electron tubes and relays switched off the darkroom lighting and switched on the enlarger at the same time. If the device was carefully calibrated, the Variomat automatically switched off the enlarger and switched on the darkroom lighting after the correct exposure time had been reached.
At the time, this represented revolutionary facilitation and state-of-the-art photo laboratory technology. The Agfa Variomat C model was already suitable for the Agfacolor positive process – the processing of color images.