Panes can be linked together. This has two main effects:
By default, when opening a new preview pane from an editing pane, the new pane is linked to the old one. This means that any changes you make in the editor will show up in the preview in real time. It also means that scrolling one will scroll the other.
When a new Backlink Pane is created from a note, it will be linked to that note. This means that backlinks will always be shown for the note that is in that pane. This is useful if you want to reference a set of backlinks but let the regular backlink panel change with whatever other note you are working on.
Linked panes will be marked with a link icon. You can hover the link to see which pane it's linked to, or click the icon to release it, so that they are no longer linked. This will not close the previously-linked pane.