It creates a temporary closeness which will encourage generosity on your customer's part.
If they were to hear their server give a discourse 
on the disgusting nature of your quesadilla, they would 
start looking for faults in their own food. Waiter 
training should provide the learner with the adequate skills they'll require to give excellent service - understanding of the product, both in terms of the food and drinks can mean they 
sell either the rib-eye or the fillet, or the house 
red or that great shiraz that would complement the fillet perfectly.