The Yi is one of a number of systems that Crowley integrated into the schema of the Qabala in his attempt at unifying the diverse spiritual traditions of the world into a combined whole. Much to the disgust of exclusivist Kosher Kabbalists who literally froth at the mouth and shake with rage at the very thought that someone could be so impudent to apply the syncretic method to their already highly syncretic system.
I'm not sure why Crowley seemed to prefer the Yi Ching over the Tarot. Maybe he thought the the multiplicity of images in the Tarot pertained to the plane of Yetzirah, while the simplicity of the unified opposites of Yin and Yang were more Briatic.
Personally I like to read the appropriate Yi Ching hexagram whenever I get a troublesome court card in a reading. It's a bit like getting a second opinion.