>
> sometimes he can use a numeric or int array, sometimes he have to
> select text array. Target type is selected by user, and cast fail when
> conversion is not possible.
>
using a some selected type (for array field) allows a processing in plpgsql.
motivation for this feature is simplification and speedup similar
requests like this
http://stackoverflow.com/questions/7711432/how-to-set-value-of-composite-variable-field-using-dynamic-sql/7722575#7722575
Pavel