Deciding on how many chat slots each Operator should receive, depends on many factors - Is it the right decision to make all 10 chat slots available to one Operator, or is it better to keep them to a minimum?
The more chats you have running simultaneously, the higher are the chances that you lose track of your chats. Experience tells us that it's better to start small if unsure. With more experience, Operators usually are able to handle more chats within a fairly short time.
You can set the number of chat slots under "Team > Operators" in the respective operator profile under "Message Center".