Just as the song of a Poke Flute can wake a pokemon in the deepest of trances, the leaf of a Nuzleaf when properly whipped through the wind can wipe away even the most dire injuries a fainted pokemon may suffer. Yet pokemon centers will only call upon the expertise of Nuzleaf for the gravest of injuries, for like a Poke Ball in reverse, a Nuzleaf's power can make even the most tame and loyal pokemon forget that they ever had a trainer.
In remote areas of Hoenn, where true healers were unavailable, pokemon training took a decisively different character. Although their culture demanded that every pokemon was given a name, trainers strove not to grow too attached to their pokemon, for no matter how hard they tried defeat would inevitably someday return their comrades to the wilderness from where they came. Instead, the people of rural Hoenn scouted the wild for what powerful pokemon would inevitably return there, and learned not how one or two teams operated, but an entire metagame of techniques; the canonical texts of pokemon strategy unsurprisingly were written in this region, although they would in time be supplanted by a university which began as a school for Koffing trainers.
When the outside world was at last linked by road to these small towns, Chansey came with the changes of modern life to replace Nuzleaf at pokemon centers. But the ways of old were not forever lost. A contest based on the ways of the Nuzleaf-healed has spread as far as Unova and is beloved by countless trainers. They must fight every gym in a region and walk the routes in between, but may no longer use any who fall in battle, to simulate how they would be released into the wild in that era.