1. They required one of us to purchase a soda (and chug it)
2. The cans only worked on asphalt and concrete. We couldn't play on grass.
3. Since the crushed cans had sharp edges, they ruined our shoes.
4. Occasionally they would take to the air and become dangerous flying projectiles.
That said, they were far more reliable than actual soccer balls, which we could buy easily from sporting stores. They didn't go flat (they already were, ha!) and didn't need to be inflated regularly.