Why Royal Navy ships kept a separate battle ensign

What distinguished a Royal Navy battle ensign from the flag used every day?

It was a specially kept, clean and pressed ensign reserved for battle, while another ensign absorbed the wear of ordinary service.

Modern Royal Navy ships normally fly the standard naval ensign rather than the personal coats of arms and command flags associated with earlier commanders. A ship could keep one working ensign for ordinary service and a separate battle ensign protected from daily wear. The latter was pressed and clean when raised for action, even though smoke, weather, and battle would soon soil it. The practice turned a familiar national flag into a deliberate signal of identity, readiness, and crew cohesion at the moment of combat.