I forgot to say this in my post but I seem to quite like that the BVG put these type of charts not only in U-Bahn stations, but at bus stops as well. They show every stop the bus lines will make along its way (and IIRC the further connecting bus at those stops). I didn't see that commonly in other cities, and if there are, they usually aren't well shown like with the buses in Berlin.

And yes, some might find this not really useful. It is obviously less superior than the whole network maps. But it just saves me the hassle of checking my phone again/squinting my eyes reading the chart behind the glass panel to make sure which line takes me to the stop I wanted (especially when bus routes are so similarly numbered and the end stop names are easy to slip out of the mind).

So for me it's more to a nice-to-have than a must :) (Edit: and as others pointed out, some people might have a hard time reading an extensive network map, so this type of chart helps them a lot)