Case in Point can be an initial step to understand how a consulting interview works (eg you will have a fit part, a case, questions at the end, you should keep a structure, repeat questions etc). Form that point of view the book can be useful.
However, the book is not good in its core part - the structures. They are simply too many, too broad and not MECE. You can use as starting point, but you should create your own structures, so far that you advance with experiences.
Thus for general usage, I would recommend the following:
1) Read it once to get a general idea of what a consulting interview is; keep track of the cases you found more challenging. Don't memorize the structures, but use them to define the basic starting point for your own ones
2) Develop your own structures with practice; to do so you can
- Do live cases with peers and
- Read cases in good consulting MBA handbooks (eg Insead)
After each case, investigate your initial structure to understand if it could have been more complete and MECE. Update then the structure accordingly.
3) Go back to the Case in Point case examples you found more challenging; apply your updated structure to solve them. Verify your updated structures are good enough to correctly identify all the key elements, otherwise continue refining them.
If you are in a hurry to learn how to correctly develop structures, you can consider hiring a coach to understand how correctly structure cases and save time in point 2. You can find a suggestion on the approach I would recommend for that on my PrepLounge profile.
Hope this helps,