Pokemon SoulSilver/HeartGold: What do "groups" do?
In the Pokemon School, you can create a group and other players can join. I created and some friends of mine joined. The NPC says something about syncing events.
What does being in a group do? What kind of things does it sync?
Solution 1:
Joining a group is a feature introduced in Generation IV. Players in the same group encounter the same swarming Pokémon, weather conditions, changing Pokémon in the Great Marsh, Feebas location, and other things each day. Group members can compare records on the third floor of Jubilife TV.
Source: Bulbapedia