One click on the red button circled on the screenshot above displays all the future appointments you have for this client for all of the client's animals. If the clinet has no appointments this button is grey, not red. The same feature is available within the patient screen. 

This is great for the front desk when a client calls because they forgot when an appointment was, or they need to change an appointment. It also makes it easy for the veterinarian to quickly see when the patient is due to come in again.

You can print the next client and patient appointment on the invoice that you hand to the client after the visit is completed (see screenshot below)