What does linkblock module do?

It is used to display links to other entities. We used that in Drupal 6 when entity reference was not really working well. Furthermore it is much more performant than other solutions. It can be used e.g.: If you have a database of persons and a database of objects that belong to a certain person, then you can do such things like "for the object I am currently viewing, show me all the other objects the person possesses." etc.

Cheers!

Thank you, Knurg!