That's a common belief that I never bought into.
Your walking around all day, so your calfs are getting thousands of light weight reps all the time. They're used to this, so why train them with more light weight reps?
I say hit them heavy with low reps - something they're not used to.
Or sitting calf raises. That's a angle they never get hit with during daily activity.
My 2cc's.
BTW my calves aren't good, so my results don't prove the effectiveness of my theory.
http://i10.tinypic.com/524hbub.jpg