The Bally Astrocade was a 1970's home game console that had 4K of RAM, and the video chip used about 4000 of that 4096 bytes to render a 2bpp display.

According to the Wikipedia article, it had BASIC on a cartridge, and that cartridge I guess had to do the following to be useable at all: set something like the 01 and 11 bit pairs to the same color, and then store program data in spread-out bits among the video data portion of the RAM. Really weird. https://en.wikipedia.org/wiki/Bally_Astrocade

Yeah, I happen to see Adrian's Digital Basement on YouTube showing how it works. When he described that, I shook my head and called myself an idiot that I didn't think of it.

Extremely useful? It's a forty year old computer.. sort of useful, maybe.