I have cheated, but I can't really call it cheating... since 'cheating' is breaking the rules to win...
I basically cheat to see levels/items/data otherwise removed from the game. most of wich is useless. here's some examples of usless things:
Wi-Fi Brother Band items in Lunar Knights (Wi-Fi removed from english version, making these items complete pointless since Wi-Fi with StarForce was needed to give them power)
Rulebook, etc. in Pokémon Daimond (The rule would change the wi-fi battle rules, but the plan was canceled (even in the japanes version), however the item was left in the game, it does nothing, however, since there was no coding added for it's planned effects.)
The stuff that actually was useful, but removed from the game I only access if it was only removed from my version bat was still in others, example:
E-Card customizing thing from BattleNetwork 3... or 4, I for got wich. (It was in the japanese version, and removed from the north american version, the coding was still intact, though.)
Any other cheating is done after I beat it once, first to make it harder, then to (in common terms) blow it to bits after I beat it on my custom insane mode.
I've given an enemy foot soldier infinate health by accident once... it was very amusing to have me try to instant kill it in one shot with my modified 'pea shooter' doing between 0-3 damage waiting for the instant death chance of 1% to kick in. Took 7 hours to kill him. I love unmodifiable special abilities of certain weapons.