i think danzo is used because of his second chase(after breakthrough) that is triggered with 10 combo, and attacks 3 people(he get wind mains chase : Wind style vacuum blast). in order to achieve the edo hiruzens chase which is triggered at 30 combo for instance if there is only 2 opponents left and you use edo hiruzen mystery (causes 20 combo ) danzo helps to add more combo.. :)

i think thats it not sure though but i watched a lot of his fight to notice that