Importing / Updating with on creation Serial Numbers

[Sunshein]

When importing records from a similar file with same related tables, is there a difference whether the linked serial number field is generated on creation or on commit?

Seems if the linked field is generated on creation, it does not keep the relationship between tables when new files are imported.

I am not sure if I understand when to use on creation or on commit for generating serial numbered fields as the related field.

Frank