Roms are used in just about everything where a PCB needs software or commands to execute. Although I have mostly dealt with them in arcade and pinball machines, there are many practical applications for replacements, repairs, or customization. Some of my customers requesting custom burns have been for:
Play hacked / customized versions of the software*
Add Free Play
Add profanity
Unlock hidden characters
Restore removed characters, glitches, and other features from previous versions of the software (Who remembers MK2 characters and the tank game in NBA JAM?)
Upgrade or downgrade software versions to the latest version or first prototype
*Please keep in mind, when I say “custom”, I mean you provide me with a rom image to burn on a chip “custom” for you…I am not smart enough to hack games and make my own “custom” versions or customize / change games for you, but there are various ones floating around all over the internet!