Exploiting things in games

Have you ever exploited a glitch or a problem in a game to either make progression or just make for a better performance?

The ATB system on Final Fantasy has some problems, that I suppose could be classed as a strategy, but nonetheless it assisted me in finally beating Sephiroth. You see I never had Knights of the Round (the most powerful summon) so I kept getting absolutely destroyed by him. I finally realised that waiting for him to attack first and then healing my party up was the most effective strategy. I almost was in tears when he started to shatter and then I quickly proceeded to laugh

I' ll probably have some more fitting ones to come whenever my brain wakes up.