When a custom object record is created it is associated with a person or company record based on the link field. When that company or person is merged with another record, where the other record is the surviving one, the connection of the custom object is not carried across to the surviving record. Instead it becomes an "orphaned" record. It would be wildly helpful to be able to carry this association across in a merge.
There are other scenarios too where it can be extremely unhelpful that custom object records cannot be corrected to associate with a different record after creation.
.png)