Here's more information about group appointments and concurrent appointments (not exactly the same thing):
1. group appointments: by setting the # of attendees to more than one, you are telling the system that a given appointment type is a group appointment type. What it does is allow x number of appointments (from different clients) to be scheduled at the SAME time on the SAME schedule for the SAME appointment type.
In other words, group appointments do not span several schedules any more than regular appointments can. Think of it as a group appointment going to a specific resource.
2. concurrent appointments: these are appointments (group or not) occurring at the same time, overlapping entirely or partially, of the same or different types, on DIFFERENT schedules.
Let's say you have 2 schedules, Employee A and Employee B and you have 2 appointment types, Service A (10 as the # of attendees) and service B (1 as the # of attendees). Let's say you have an open slot on both Employee A and Employee B's schedules at 10 AM (and both services can be scheduled). As soon as Service A is scheduled at 10 AM with Employee A on that date, only Service A appointments will be available on Employee A's schedule for the same date and start time (up to 10). Employee B's schedule remains unaffected and both Service A and Service B can be scheduled at 10 AM on that date. As soon as Service B is scheduled at 10 AM on that same date with Employee B, the slot will disappear and nothing else can be scheduled.
So we could have 10 Service A appointments at 10AM on Employee A and 10 Service A appointments at 10AM on Employee B for a total of 20 concurrent appointments.
Or we could have 1 Service B appointment at 10AM on Employee A and 1 Service B on Employee B for a total of 2 concurrent appointments.
Or any other variation thereof :)