Two regular employees, Tom and Lalitha, normally sit at their own desks to perform their job, but may occasionally act as an in-bound call agent when a regular agent is out sick or on vacation. ACME handles this situation by creating a device group, ACD Substitutes, and assigning it to the worktops used by Tom and Lalitha.
As an alternative, you could allow Michael, Sally, Juan, and Marie (the inbound call agents) to switch desks by assigning the ACD Substitutes list to the secondary device group on each worktop or by assigning the list to the Call Origination and Termination group and Device groups in each of their user profiles.
ACME also shares a worktop in its shipping department where Louise, Frank, and Susan work. There is only one worktop in this department and all three share it.