Getting better at the game more or less. It's one thing to watch replays and try to learn from them, it's on a completely different level when you're able to see what people are doing behind walls all the time in realtime. Saves so much time compared to watching replays, who has time for that? Plus it doesn't stick as well as immediate feedback. After a few dozen hours playing competitively on a particular map with wallhacks, knowing how people generally behave in specific situations gets baked into your brain. Then you turn the wallhacks off and play better, at least that worked for me as a kid. Now I only really play single player shit or things where cheating either doesn't matter or makes the game worse.