Like i said, people can be dps wrong targets, healers can miss to cleanse, people can miss interupts.
Theres so much more info u can get more then just dps, most fight the dps dont even matter its just a matter of people doing the right things in the right order and a addon to see what people did makes it alot easier.
Can it be done without it, well ofc but why make it harder then i have to be?