Custom firmware enable you to run packages on your PS3 that are unsigned,
in other words you can backup your games, play with emulators, create and
play your own homebrew and more.
If you have a playstation and you are currently on OFW (Original Firmware) 4.21 you are in luck,
your playstation will be worth a lot more if you leave it @ FW 4.21 and never update.
My ps3 has been worth 600 dollars for years because of the model # and the fact I never updated
it past FW 3.55 up till now (because its safe to update to 4.21 from 3.55 and back if you have
the kind of PS3 model I have cecha01).
Edited by FiveSixDeuce, October 22, 2012 - 05:37 PM.