This multiInstantiator works with a String input variable. According to the separator you define, it splits it into a serie of tokens. It instantiates the task n times passing to each of those tasks one token.
It is also possible to define a threshold (in pourcentage) to control how many tasks must be realized to continue the process (by default 100% - all of them).
Use case : I pass a string "guest1, guest2, guest3" with the seperator ",". the multi instantiator will instantiates 3 times the task it is linked to and pass guest1 to one task instance, guest2 to another etc.. If I have defined a threshold at 50%, the process will continue after having two tasks finished.