Multisport is primarily used in Triathlon, Duathlon, Swimrun, Multisport and similar. I use it a lot. Start a run, then during the run I switch to swim and back to run and so on. The watch automatically creates a multisport activity with a multisport time and distance.
You don't have to create a workout in advance to use the watch and I believe that the majority of all users don't create workouts at all. They just go for a run or ride and that's it.