Have you ever asked the guy selling you the movie ticket for advice on what to see? Asking a waiter's opinion is no different imo. You haven't the faintest idea what their personal taste is so their opinion may be totally off base to what you want. It is also possible that the person serving you has no interest in food and works their to pay the bills. I'm with Clint. The only time I ever ask is if I can't decide between two dishes and I'll use their opinion as a coin toss.

I think what Clint is saying, a bit more bluntly, is they are employed because of their service skills not their ability to make dining recommendations.