When you and your pair partner work on your partner's task (PairProgramming, of course), you are accumulating a PairingSurplus. If you accumulate too high a PairingSurplus, you're artificially lowering your velocity (because you are spending more time helping others than doing your own work). You reduce PairingSurplus by pairing on your task. Spending too much time on your task leads to a PairingDebt.

A high PairingSurplus may or may not be a bad thing, especially if the resulting PairingDebt is spread around the team (as opposed to being all with one person). Certain ExtremeRoles, such as the Coach, will naturally have a high PairingSurplus. 

The downside to a high PairingSurplus is that you won't be able to sign up for as many tasks as you could do in an iteration, due to YesterdaysWeather and your artificially low velocity. This assumes that you use individual velocities during IterationPlanning, of course.

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