A good rule of thumb is that the more space a case takes up in a casebook, the more important the case. This isn't always true, but it's generally a good idea not to do 30 pages of reading for a case that's been edited down to one paragraph. If the case is just a note or there to introduce a topic, etc. then your professor might not even bring it up in class. I don't recommend using Lexis to look up cases unless they're 1)important 2)you're interested in it, or; 3)it's con law. I think it's a rule that all con law casebooks have to be poorly edited and confusing, so I used Lexis briefs a lot.