When my doctor doubled my dose of Lexapro, she didn't give me a new prescription right away. I was due to run out of pills before my insurance would cover a refill because of this. My doctor was pretty cool about it, and gave me a weeks' supply in free samples.
I can understand why drug companies give free samples of certain drugs to their patients. I'm not sure why they give free samples of Lexapro to my doctor, though; Lexapro takes more than a week (one sample's worth) to take effect, and it's dangerous to stop taking it without a physician's advice. In this case, it was handy for me to have the spare pills, but I don't think that's what samples are intended for.
Of course, drug companies do much bigger things to sway physicians and patients.