To expound on Dark Venusaur's correct answer, when you start out in FRLG your traded Pokes will only obey you up to Lv10. From there, for every two badges you earn, the Level your Pokes will continue to obey you increase by 20. That means:
2 badges: Lv30
4 badges: Lv50
6 badges: Lv70
8 badges: ALL
I love this idea since it prevents people from cheating, starting off with a high level Poke and breezing through the game. It helps bring some sort of balance to the game, despite the continued lame AI tactics.
BTW - This should have been asked in the Simple Questions thread. A Mod will most likely close this topic.