My opinion is that they are the worst idea ever created. They incentivize infighting and undercutting each other. They lead to situations where everyone on your team is a top-notch performer but you have to cut someone, so you fire someone who's doing a great job. Or the reverse, everyone on your team is a complete fuck-up, but you have to give bonuses to the top 10% or whatever, so you reward people who are doing a terrible job. Nobody I know who has been involved with them (including the managers who have to do cutting and bonus-giving) thinks they're a good idea.