Space is an important design aspect with web applications. So, a component that allows hiding certain content on a web page during runtime is of a great help. The collapsible panel is one such component.
Besides the hiding of content, collapsible panels are also a means to visually group components. In a lot of cases, it is useful that we group something and also hide it.
If you combine these design ideas with a session-spanning persistence of the hiding state, you get a self-managed user interface behavior.
The ICEcube sample page for the collapsible panel looks like this:
The screenshot shows two panels, both in a closed state. ...