It generally seems odd to me, but at my job we used to go at lunch time to a place which didn't do this, and they would simply lose one person's order some of the time (i'd say 1 in 10). It's really annoying to be the one person whose food hasn't arrived yet wondering for ages if they are being slow or have forgotten. This extra touch gives them the opportunity to find out that they forgot something without completely pissing off the customer.
