Screenwriters : There are comedy sketch groups where…

There are comedy sketch groups where…

... each member has the same task (acting and/or writing and/or directing) every time. There are also groups where they take turns. Which of these 2 types of groups is more frequent? Also, if the group is formed when members are hired by someone (rather than when the members are friends who decide to work together), does that someone assign all the tasks every time?
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