A deep, throaty voice is something that practically any listener or viewer will notice immediately and in most cases, pay close attention to what such a gravely voice hast to say.
In "The Dead Don't Die," one of his more recent movies, director Jim Jarmush uses singer Tom Waits and actress Tilda Swinton as narrators that deliver their lines, as one comentator notes, as as a gravel-voiced narrator (Waits) and samurai sword-wielding Scottish undertaker (Swinton). Reaching for such deadpan, gravely voices, the director obviously got exactly the effect on his audience that he wished for. Such a specific voice seems to have a remarcable effect on listening/viewing audiences in any context they are used.
When you need to create the effect that the voice speaking knows exactly what she/he is talking about due to a longstanding experience with the subject matter, a gravely voice is probably the one that leaves a deep effect. It is usually an audience that needs some serious arguments to be presented to it so that it can be convinced. A gravely voice usually creates such a convincing effect.
A gravely voice sounds deep, deadpan, well-weathered and often rough at the edges. While such a voice is often connected to male characters, female characters can also have such vocal characteristics. A gravely voice usually speaks very slow, enunciating practically every word it speaks, giving it an additional sense of meaning. While gravely voice often depends on the natural vocal color sometimes tied to age and experience, vocal practice can help create a gravely voice too.