There are few advantages doing it in Entity Layer.

1. If there are five VO's created using one EO, it would act as a common maintenance Object.
2. If in future there exists a need of mapping this transient attribute to a DB column so that value could be persisted, the only way to achieve it is via EO Layer.
3. Being created at EO layer,it helps in entity cache which can be consumed and shared by view objects.