[vannevar]

A day rate can certainly work against you, in the same way that salary can work against you, if there's more work to be done than can be fit into X number of days at 8 hrs/day. You may end up working 12 hour days for the duration. I think the convenience of a day rate is more about not having to track work at a tight level of granularity, and having a guaranteed minimum per day, than it is about pocketing efficiencies.

[seanwilson]

One of the core benefits I think of fixed price is you have a large incentive to be efficient, which you don't have so much with hourly, daily or weekly billing. Do you know any other payment structures that encourage efficiency in the same way? There's milestone based billing which is similar to fixed price but requires more planning.