Not until your playing doubles and you get hit with your partner's racket while he's serving.Jake, there are many ways to interpret "as loosely as possible." No one should suggest gripping the racquet hard either. That would lead to injury and disable any possibility of fluidity in a swing. Most tennis players don't even keep their entire hands on the racquet. If "firmness of grip" were the answer this would not be the case. One should only grip the racquet as firmly as necessary. On the serve, I would suggest the grip is looser than on ground strokes. One is not having to absorb the impact of the oncoming shot, and the full arc of travel is the longest of any swing, putting a premium on fluidity. I'm not suggesting that you believe anyone should strangle the racquet, but I don't have any issue with what he has said.
I've seen this more than once. Part of an instructors job is to limit liability and prevent injury.
Yes, I hold my racket with only the butt when I serve, however, I'm an advanced player and developed this over a period of time. You don't teach this. You can mention this, generally a player will "grow" into it.
That guy has no idea who he's talking to and doesn't care and you're defending him?
Pat your dog.