This is from Microsoft Office Access 2003 Inside Out:

If you build a table with a primary key that is Text or Number (perhaps a
ProductID field that could change at some point in the future), it might be a
good idea to select Cascade Update Related Fields. This option requests that
Access automatically update any foreign key values in the child table (the
many table in a one-to-many relationship) if you change a primary key value
in a parent table (the one table in a one-to-many relationship).