I remember being happy with the cheat functions on the C64 until I grew up and found I was ruining bunches of things for myself. Some cheats ruin the game more than others. Infinite lives is a thing you might use in very hard games. But to take an example, Tilt! (By codemasters I think, the one where you tilted a board to make a ball roll around it, anyone seen an Amiga version of that?) had a cheat mode, which if enabled, allowed you to go through walls. I seriously had no idea about what the game was all about since I'd just turn the table and move the ball into the hole. It was such a lame game I thought.
Then a year later after I had rid myself of the nasty habbit I decided to try again (mostly because I had forgotten what it was), this time I didn't cheat and I loved the game. You have no idea how many hours I spent on that game without completeing it. I think apart from Park patrol (which was the first game we got for the C64 so I had nothing else to play) Tilt was the game I spent most time on in total. The fact that the cracker would make a "cheat like this or don't cheat" option really made me sad.