It depended on the laser printer. It's funny that the poster mentioned Xerox laser printers in particular because cm looked especially bad on them: There were two competing approaches to laserprinting. One was write black where a laser was used to add charge to the parts of the drum that should be black. The other (used by Xerox and perhaps others) was write white where the whole drum was charged and the laser was used to remove charge from the parts that should be white. In either case, the pixel was a little bigger than the actual 1/300in x 1/300in square that was to be drawn so it resulted in CM coming out even more spindly on write white laser printers. Neenie Billawalla came up with a modification to the MF source code for CM to allow for increasing the darkness of the fonts as well as some other fine-tuning. (https://tug.org/TUGboat/tb08-1/tb17billawala.pdf)

As I recall, there were occasional other issues with running MF on the CM sources at low resolutions and it was often necessary to just tell MF to continue at the error prompt to generate the font (when Tom Rokicki's dvips incorporated auto-running MF to generate missing PK files for specific resolutions, I think it ran it with a default setting of ignoring errors).

Those 1980s Xerox laser printers were real beasts. The 87xx/97xx series printers were prone to rolling over (crashing) on TeX print jobs since downloading fonts to the printer was not fully supported. The first dvi driver for the Xerox printers actually required pre-installing font sets on the printer and only certain combinations of fonts could appear in a single document. I don't think the 27xx series printers were ever capable of handling TeX output.