What does the pushpin do
From Support Wiki
When the pushpin is in the “stuck” position, the section will always be open by default each time you log back in. Click the pushpin to change from open to the closed position.
The pushpin does not affect the default position when switching between tabs or users. Think of it like you are “resetting the areas back to default open/close position” every time you login. During your time logged in, you can open and close the areas as desired regardless of the pushpin status. The pushpin only affects the initial position of these areas when you first log in.