With printers from Kyocera you can store font-files, macros, "PRN files" and the such on the Compact Flash card. Insert it as described in the manual and fill it wit Kyocera's "IC-Link" utility.
As for the font-files, TTF is among the supported formats. If you have, for example, PFB or OTF ones you can convert them using the free open-source software FontForge.
Storing them on the printer (CF, memory…) will theoretically speed up printing lots of small documents with different fonts, because your PC can skip sending the fonts along with the document. You will notice a benefit only for very large ones, though — the most popular fonts/typefaces consist of just a few font-files with about 50–120kb and your printer is most probably connected by a relatively fast connection capable of transferring them in milliseconds.
Another use-case for a CF card are "PRN files". That's basically frozen print-jobs (most probably forms or pamphlets) which you can replay without your PC, using the printer alone.
For current Kyocera printers, you can store up to 256 different resources on the CF card. Speed of the card doesn't matter, because the bottleneck is the printer which reads/writes them at about 0.1 MB/s — max. Unless you use very large font-files (e.g., typeface FFF Tusj) you will barely fill 30–40 MB of your CF card.
Print-jobs are not cached using the CF card. For that you can have your printer create a RAM-disk in internal memory. The effect will be that your print queue on the OS will be empty sooner, and multiple copies of large documents will print faster. (A single large print-job won't benefit from the RAM-disk at all. To the contrary, it might get not printed at all if it doesn't fit into the RAM-disk. If in doubt don't use one.)
Fonts are cached in internal memory, too, once sent by your operating system. Therefore, if you really want to pimp your printer, better buy more internal memory.
