Layouts are automatically saved when an autoSaveId prop is provided. Try this by editing the layout below and then reloading the page.
1 <PanelGroup autoSaveId="persistence" direction="horizontal">
2 <Panel>
3 left
4 </Panel>
5 <PanelResizeHandle />
6 <Panel>
7 middle
8 </Panel>
9 <PanelResizeHandle />
10 <Panel>
11 right
12 </Panel>
13 </PanelGroup>