This value reports the size, in bytes, of the binary firmware image currently running on this card, per the description. An admin would check this mainly to confirm a firmware transfer or upgrade completed with the expected image size, or to sanity-check available flash/storage headroom on the card before attempting to load a newer, potentially larger image. A size that doesn't match the vendor-published size for the swRevision-equivalent firmware version would suggest a corrupted or nonstandard image.