I do this too. I just finished The Three Musketeers because I have tickets to a theatre production in November. I thought it started off okay, I was pretty unimpressed with d'Artagnan. But half way through I thought it got really good. Now I'm just hoping the show sticks to the first book because I don't have time to read the rest of the trilogy. I find knowing the story ahead of time adds to the enjoyment of live shows, you can see what's been adapted and omitted for the stage.