To add John's answer, in general terms, on WikiTree we think of families as overlapping circles. Some large, some small. Not everyone in "a family" is interested in the same indiviiduals or the same depth of genealogy. You might want access to a sibling or cousin's profile, for example, but not all his ancestors from the other side of his family.
The way we manage privacy controls on the individual profile level is actually essential to how we balance privacy and collaboration on WikiTree. It's what enables us to all share one, worldwide family tree.