The succubus can deal more damage than an Imp and can continue to attack if she runs out of energy, but cannot take as much damage as a Voidwalker. The Succubus also cannot hold aggro as well as the Voidwalker. Her armor would be rated as "Medium" compared to the Voidwalker, and she has the same amount of health as the Felhunter; less than the Voidwalker but more than the Imp.
The succubus is particularly useful on enemies of a lower level than the warlock due to her higher damage output than the voidwalker.
Because of her Seduction power, the succubus is a very useful pet for a warlock in most PvP situations. Her Lesser Invisibility power is also very useful; opponents will underestimate a warlock whom they believe not to have a pet out.
Her [Seduction] power is channeled, which means she is out of the fight for as long as her seduced target is.
Whiplash can be used in an emergency to get dangerous enemies away from the warlock. Beware of disrupting a tank's positioning of the mobs in a dungeon or raid, though!
It's easy to think that Lash of Pain is a melee range ability, but it actually has a generous 20 yards of leeway. This allows her to chase enemies much more effectively than you'd think.
Voiceovers when summoned:
"Couldn't resist, could you?"
"Hmmm, you're in trouble now."
"Don't touch what you can't afford."
Voiceovers when ordered to attack:
"Let's have some fun."
"Being bad never felt so good."
"Let's get this party started."
"Now you're talking."
Voiceovers when ordered to cast a spell:
"Quid Pro Quo."
"As the master wishes."
"You got it."
Voiceovers when dismissed:
"Next time, I'll be the master."
"Don't do anything I wouldn't do."
"Try not to miss me too much."
"I hope it was good for you."
"First we'll start with a little fire. Am I bugging you, I'm not touching you, am I bugging you, I'm not touching you. There - now you're hot AND bothered."
The succubus has a rather notorious idle animation set. She will on occasion either pose, admire her nails, or spank her butt and let out an erotic squealed "Oooooh!".
The unique swimming animation for a succubus is, perhaps unsurprisingly, a form of breastroke.
When you target the succubus with a /flirt or /kiss, a heart will appear above her head for a short time. This effect has a cooldown and is not reflected in the combat log but will disrupt invisibility until it can be recast.
When incubi were requested as a warlock pet, Zarhym responded that Blizzard had plans for offering players a choice between male and female versions of all warlock demons. They are commited to making this happen, but they don't have a time frame for when it might be implemented.
The Succubus appears as a basic card for the Warlock class in Hearthstone. The flavor text reads: "Warlocks have it pretty good."