Bring on the understudy! Does it matter if the star isn't in the show?

As James Corden fans waiting to see One Man, Two Guvnors in the West End now know, the big-name actor may not be the one you see on stage. But sometimes these performances are the best You've cleared your schedule, hired the babysitter, fought the crowds, taken out a small loan to finance your ticket purchase, and have finally settled into your plush(ish) seats to await the latest Broadway or...