Which would pretty much mean that Series not only has an Owner, but also Contributors who can, after being invited, add their own pieces of roleplay to the Series.
Useful when, for example, you create a general text repository for your world building that goes on with another person - you can add spin-off little stories and other pieces of information useful for people interested.
Related to Allow series to be set as public because it allows to actually use the series or anything.
Related to Permit editing of a series (to delete RP from it) for moderation purposes.