Tabletop exercises are a useful tool for developing the skills to operate in a real-world situation, with the opportunity to identify many challenges and pitfalls before ever going through the effort of staging an actual exercise or deploy to an actual disaster.
Why tabletop versus a Simulated Emergency Test type exercise? Well, they are easier to plan and execute, all you need is a meeting place, and even the table is optional! Trying to coordinate an actual drill may require coordination with served agencies and place demand on physical resources like repeaters, radio equipment, or even served agency locations; all of this takes time and often places demands on other organizations.
Tabletop exercises can often be executed in an hour or two, where actual drills typically run much longer, placing more demands on the time of volunteers.
Tabletop exercises provide an opportunity to develop a plan or just work the bugs out of existing plans by playing "What if" games and talking through option when dealing with mission critical information such as knowing primary and backup repeaters, what to do when repeaters are down, frequencies and timetables for simplex communication, etc.
