There are tables that are used for quick data entry that are normally not updated very often (for example product brands). The linked table GUI allows to pick existing records from the brand table, or if you type new stuff and press enter a new record is created in the table. During massive and quick data entry this can be a problem as duplicate or incomplete records could be created. The idea is to have a “flag” at the table level that updates to that table can only be done from the actual table, and not from a linked record. It is a “data validation” feature really.