Aside from the sexual, what else can you gain from them? Ive not heard of them before until I joined this forum
Anything and everything. They are spirits close to the physical, and can help in spiritual Ascent by opening chakras, manipulating energy, helping with astral travel, and aiding in your magical rituals. They can make contact with other spirits easier by acting as a mediator and they will defend you as well. They are companions, lovers, and wives.
Every succubus is different, with different skills and talents, but the sexual bits are but a small part of what they can do.