Rooting is one of the highest-priority behaviours in pigs, and providing appropriate rooting substrate - whether indoors or outdoors - is a fundamental welfare requirement.
Rooting is not a preference but a need for pigs. Depriving them of rooting opportunities creates frustrated animals that redirect their motivation onto pen mates, causing injury. Providing adequate, fresh rooting material fulfils a fundamental behavioural need and is one of the most cost-effective welfare improvements available.