Chess books with exercises

I just bought Jacob Aagaard's book Grandmaster Preparation:Calculation. Calculation is my strength compared with say positional play or strategic play, but I am able to solve a few problems all on my own and without even taking much time. I find even the examples helpful even if I cannot solve them. They stick in my mind.

What in your opinion are the benefits of doing exercises. I feelthat when you are trying to solve an exercise many things happen in your head. You exert yourself hard and if you're not able to find a solution then after looking it up you figure out exactly where the fault was in your thought process. Hence it makes you aware of your mistakes.