When you want to use the Canvas to actually link between the elements whether they be notes, headings, blocks.
With the true link mode enabled, dragging links between canvas elements would add directional link based on the drag direction. There could also be the ability to alt/option drag links between two notes to add bidirectional links.
While in this mode, clicking on existing connection lines would make them true links. It would be helpful to some sort of visual distinction of connection line color.
There could be additional settings for how the links are inserted into notes and headings, but perhaps by default they are simply added on new line at the end of the notes and headings.
I saw this post in another thread serving a different context, but felt that it was definitely relevant here. The two YouTube videos that are linked to are worth checking out. On the first video, the relevant part is towards the end.