It gives you the opportunity to give her more stimulation, stimulate her simultaneously internally and externally, and provides her with lots of variation.
The clitoris itself extends a few inches further back into the body.
Use your tongue at first to enhance arousal and then a finger to complement and push arousal to the next stage.
I used this technique on my Saturday morning delight yesterday and although I had done similar things in the past with her.
Idk if this factors into it.
Some orgasm best from tongue circles around the clitoris, others prefer a light sucking motion.