The advantage to more confirmations is that more blocks have been found, meaning it's that much harder for an attacker to outpace the truth. You can accept 0 confirmations if you want, but that's generally considered riskier than any higher number. Small amounts may be worth the time savings, like if you sold a Coke to someone. They are very unlikely to go and attack the network to double spend that amount. But 1,000,000 BTC.... A different story.