Hourly work vs. linchpin work

There's a gulf between hourly work and linchpin

work.

You should pay people by the hour when there are available substitutes. When you rely on freelancers you can put a value on their time based on what the

market is paying. If there are six podiatrists in town, and all can heal your foot, the going rate is based on their time and effort, not on the lifetime use of your foot.

On the other hand, if there are no short term substitutes, then you don't pay what the market will bear...