Folgezettel is a hierarchical placement of notes in Zettelkasten (i.e., a single hierarchy as defined by note ids). It does not imply hierarchy of ideas—just their proximity and obvious connection.
It is arguable if it is useful in digital Zettelkasten or is only necessary in physical one.
Provide overview of thought trains by placing notes close together
Notes proximity deteriorates when new notes are added between existing ones. Thus, proximity can be lost over time. (Structure notes seem to provide a better
Make related notes easier to fetch from physical Zettelkasten
Obviously does not apply for digital Zettelkasten
Provide stable ids
Time-based id in digital Zettelkasten might be even better
Initial placement might be rendered irrelevant in the future
Structure notes (to provide overviews) and direct links (to establish connections)
Discussion of Folgezettel: