The fact that I didn't have to create my own lists was great! They gave me very specific instructions about what they were looking at in order it be properly cleaned up- nothing too confusing there!! It also helped us avoid having our data misused by others who had no business doing so since we are not giving them access unless asked directly first (which would then require their approval).
We've been able get rid off many people from certain accounts as well which has really saved time because now those folks don’t needlessly clog inboxes every day when reaching out via an auto responder etc..