Once I found out about the item and Pokémon cloning glitches, I put both to extensive use. I used the MissingNo. glitch (R/B) extensively to clone Master Balls, Nuggets (so I could sell them and eventually max out my money), Full Restores, and Max Revives.
In Gold and Silver, I frequently used the Pokémon cloning glitch to duplicate rare and legendary Pokémon, including those I had imported from Gen I via Time Capsule.