I have an older Postscript laser printer with resident fonts and they were typically provided that way for several reasons, among them:
1) Resident fonts were stored in ROM and didn't take up (afaik) the printer's memory during printing. This could make the difference between printing and not printing on a complex document that used up a lot of the printer's [limited] RAM.
2) On a slower connection (parallel or serial), a print job would print faster if it didn't have to send the fonts to the printer instead of just the raw Postscript / PCL data.
Typically if the document fonts have the same name as the printer font name, they will be substituted. You may have to create a mapping for this. In e.g., a2ps, you can set them in the prologue file: a2ps documentation