2-Linked is a directory for your linked prose. It is within Org’s secondary search scope. (This means opening org-id links will work.)
Directories are searched recursively, so use as much tree depth as you need.
Org link search finds GUIDs (Globally Unique IDentifiers) in 1-Agenda and 2-Linked. Org agenda search only finds headings in 1-Agenda.
Org-id searches can rely on cached results, whereas Org agenda searches normally do not. Therefore 2-Linke can store much more text than 1-Agenda, without causing excessive Emacs lag.