When devising what became Smart Objects in Photoshop, we had several goals:
- Enable non-destructive transformation & filtering
- Tighten integration with Illustrator & other apps
- Facilitate “edit one, update many” parent-child links among layers (a la “symbols” in Illustrator, Flash, etc.).
The last of these is far & away the most obscure and, frankly, confusing. Photoshop doesn’t present any indication about which layers are linked to which others, and it doesn’t offer a Library panel for managing SO’s. (There’s so, so much potential yet to be unlocked here.)
In any case, Julieanne Kost uses a real-world example to demonstrate how to link Smart Objects together (simply duplicate them on the Layers panel) and how to duplicate & unlink them.