Sometimes your project may call for more than just "a little soul." The hoarse, breathy rasp of a gravelly voice can be the perfect way to imbue a character with their own lived-in, gritty style, and also convey a lived-in strength and authority.
A good rasp can give a voice uniqueness and character. It's a phenomenal tool for singers all the way from country or gospel to rock n' roll, especially when they want to bring in a more soulful, authentic qualiity to a vocal performance. Characters in fiction with raspy voices tend to be more interesting, and have a slightly off, menacing quality about their vocal deliveries. A gravelly voice takes all of these characteristics to the next level and amplifies them tenfold. From the voice of a Caped Crusader hunting criminals by night, to the tortured croak of a drunken poet extraordinaire like Tom Waits, a gravelly voice is a hoarse, strained, scratchy sound that can express authority, experience, a hard life, and an extremely intimidating edge.
A gravelly voice can be a perfect vehicle for the deep, reflexive lyrics of bards like Leonard Cohen, Tom Waits, or lionesses like Janis Joplin. It's a great literary tool, ideal for audiobooks with a rich, engrossing plot that require a soulful, experienced voice to bring the narrative together and draw the reader in. A gravelly voice is also an asset for superheroes and villains. Even though it's been parodied a million times, you probably wouldn't want Christian Bale's Batman yelling at you while he's dangling you by the ankle from a tall roof.
Deep, hoarse, scratchy, and unmelodious.