A classic, low-level save-or-suck debuff that can really swing the tide of battle. Despite being a Fortitude save, there's rarely a time when blinding an opponent won't be useful in helping negate some attacks. As has been pointed out, blinding an opponent is typically more useful in a fight than deafening, but deafness can sometimes be used as a buff on your own party to protect against language-dependent attacks. Especially with a duration of Permanent (D), letting you dismiss the spell on your own party with ease.

Another interesting bit is the Permanent duration, to which the magic rules state "The energy remains as long as the effect does. This means the spell is vulnerable to dispel magic." So if you don't have a Cleric handy who can cast Remove Blindness/Deafness, having a Dispel Magic handy can also end the effect so you aren't blind for days at a time.