MAME images are literally dumps of the original data from the hardware, be it CHD for harddrive images or BIN for binary files contained in ROM chips. (usually ZIP format because there is usually a pile of ROM chips with each having a portion of the data... so containing several BIN files)
the whole point of MAME was to take the original data from the games and use it on emulated hardware. to do so you need the original data from the game.
so if you have a game with a bad ROM chip, you can download (from someplace) a mame dump of that game... find the appropriate rom image you need in the package... and dump that on a blank chip. presto bango, you are up and running again.