This table is used to relate item ledger entries to the associated posted document line when carrying item tracking.
An "ordinary" posted line not carrying item tracking will always be related to only one item ledger entry, and this relation is managed by registering the entry number in a field on the posted line, for example the Item Shpt. Entry No. field on a posted sales shipment line.
However, from one posted document line carrying four serial numbers, there will be four item ledger entries and, therefore, the Item Entry Relation table is needed to manage the one-to-many relation during posting and lookup.
The "ordinary" relation field on the line will be empty if the document line carries item tracking.