It means almost an order of magnitude less divisions (and additional calculations as well).
Quake had to do this because it would have been too much especially for a low-end Pentium when it was released in 1996.
Yes it is not even noticeable, especially at low res.
Afaik, Quake does not do one divide per pixel, it is in steps of 8 pixels (see dscan.c in winquake). Yes, there is non divide but instead of taking hundreds of cycles, tables and other approximations could be used.
Of course, div/vdiv which take only 14 cycles or less are a strong boost on CM4/33.
The LCD internal memory is write only and it is used just to hold the image being shown. Unlike the GBA where the video RAM is like a GP RAM, just slower.
It's even simpler than this. On the "pregnancy test" Doom is actually running on a pc and the scaled video is sent via usb to the replaced microcontroller which drives the replaced display. Source: https://mobile.twitter.com/Foone/status/1302834931421175809
Lots of people trying to compare our 10k-year old technology (200 years if we talk about machines, even less if we talk about robots) with something that evolved basically with billions of trial/errors in millions of years.
At this point we should check which animal can travel as fast as a shuttle and go back and forth to the moon.