Some people on Facebook or LinkedIn choose to hide their friend or connection lists. I don’t have a problem with this, and indeed I use many of the ever changing Facebook privacy settings to hide information from people.
On sites like LinkedIn the value is (supposedly) the connections, and when someone has hidden theirs, but can still see your list of connections – that feels inequitable.
As an addition in the sea of privacy options, a checkbox that says “stop people seeing things that they don’t let you see” would help things feel a bit more balanced.