Depends on the game, but if I like it, I will never say I completed it when I used cheats.
In Fallout 3 I made my own mod, everything can be repaired by basically all the "clutter" items(tin cans, superglue, scrap metal) I can use a huge bobblehead to give me 1000 ammo of every type, I increased walking speed by nearly 50% and I've installed a mod that increases weapon damage, health it adds a perk that gives me multiple perks at once(regeneration, no addiction, increased stats, breathe under water)
In Oblivion I did the same as I did in Fallout 3, but because I had a lot more knowledge of modding, I had made my own flaming sword(flames were actually on the weapon and only appeared when the weapon was drawn) which just destroyed anything it hit.(instant-kill script on the weapon)
For me, cheats add replayability to a game. As I showed above, I will use weapons in an RPG that completely unbalance the game(starting with Excalibur2 in FF9) I will use god mode and unlimited ammo in any shooter but I will always, at some point, finish the game without cheats.