Being able to read the guest's emotions is a huge part of the job of being a waiter. In event staffing, you need to be able to accurately feel your guest's moods in order to know how best to approach the table.
If a waiter detects that the guests at the table are in the middle of an argument, or they are in a bad mood, they may adjust their "bedside manners" to give the guest more space so they can possibly calm down and improve their disposition. Then on the other hand, if the guests seem to be in a great mood and have very positive feelings, then the waiter can engage more fully with the guests and create a stronger connection. When the guest feels trust in the waiter, they are more likely to take their recommendations on dishes and drinks, and this increases the odds of the waiter being able to upsell.