Blind gamers with no vision use the sounds that represent the characters movements, special moves or actions (such as taunts in games like Batman: Arkham City’s fights with thugs) to orient themselves and act accordingly.
Sightlesskombat, via sightlesskombat.com
Distinct sound design is useful for all players, but can also be an extremely helpful reinforcement when it is difficult to distinguish things by other means.
Some games can even be playable by gamers who have little or no vision at all, if key sounds are all distinct. A famous example is Brice Mellen, a blind from birth gamer who defeated Mortal Kombat creator Ed Boon at his own game.
Sometimes audio cues for all important visual information would be too intrusive for sighted players. Options can be helpful for this, for example Injustice’s mode to add extra environmental audio extra cues.
Best practice example: Injustice
Best practice example: Killer Instinct (video)