YAY! INTERNET'S BACK UP!!!!!!
I personally don't use anything like that . . . EVER(except when I used a GameShark to give myself 2000+ Battle Points in Pokémon Emerald)! They can MAJORLY mess up your game. I should know. I saw a video of SM64 with a GameShark being used. Everything was a mess of sections from different objects(walls with ! blocks, Mario looking like Luigi, Mario having a big fist, etc.). The game was also lagging quite a bit and Mario's moves were so exaggerated that if he was to jump, he would go right to the top of the level. Never use a GameShark. You will regret it(except maybe if you need Battle Points :) )