Alias Table vs Duplicate Table

Recently a fellow OBI beginner asked me whats the difference between an Alias table & Duplicate table.
And why can't we use Duplicate table instead of an Alias table.

  Well the difference here are,

Alias Table	Duplicate Table
Its a mirror image of the Parent Table	Its a Copy of the Parent Table
We can't edit or modify Alias Table	We can edit/modify/delete columns in Duplicate table
Changes made in Parent Table is automatically reflected in Alias table	Changes made in Parent table are not reflected in Duplicate table
Used : When there is a need to avoid self-join or circular join	Used when there is a need to use few columns of Parent table.

Its always good to use an Alias table, as it is more convenient in maintaining the RPD .