I tried it on my orientation cases, and I actually really liked it. I ended up getting one of those 8 packs of sharpie highlighters, so I changed the color scheme around. I like that I can just flip the page and say, "Oh, there's the holding" or whatever, especially a week or so after I've done the reading.
One thing that was beneficial for me was that I had looked up the case in my commerical outlines/online before I read the case. This gave me clues on what I was looking for so I could understand the case more thoroughly. Then I read the case once through, then did the highlighting. I feel like this method allows me to understand the case...the highlighting is just helpful to jog my memory. I don't want to get caught in a socratic method duel with the professor and just completely blank.
Although, it'd be wise to just do things however they work for you. Just a few ideas on what seems to be helping me. Granted, I don't have any grades yet to see if it actually works.