I am asking because I see something resembling a dissonance. Legendary Pokemon, as we all know, cover boxart (all main game boxart since G1, in fact), they're central to the plots of movies, and they bring customers into stores for giveaways. Yet in terms of what they offer in gameplay, what is it? Those Legendaries you can get before a game's Elite Four will make that sort of battle a good deal easier, when the "story mode" of these games is already pretty easy if you know what you're doing. Then you've got the Legendaries you catch "post-game", when many battle events left lock Pokemon levels, and ban Legendaries as a result. Likewise, multiplayer tournaments do.
So for whom or what are these Pokemon?