It's most commonly useful for facing your fears and sparking creativity. And according to some info i've read, people can practice mechanical skills and things like presenting a public speech. Although i don't know how accurate mechanical skills are because of dream physics, mental barriers are easily a good benefit that we can use lucid dreaming to handle. Someone afraid of heights can lucid dream and intentionally put themselves in a safe environment that would be very close to the real thing (heights but it's totally safe since it's a dream and you can't get hurt), so that's that.