Stone chips may be the biggest
actual problem, but it's not the biggest
potential problem.
I don't like drafting & don't recommend it. There's no argument it works to reduce fuel consumption (have you seen the Myth Busters episode?), but I don't like to give up the ability to see ahead.
From a defensive driving perspective, when you draft, you more or less hand control of your vehicle to the driver in front of you. If s/he brakes, you're pretty much
forced to immediately brake also. It's reactive vs. proactive.
This subject came up in a thread last week:
Drafting off center?