- With some customers with large budgets and long projects I found that hourly quotes gives me a quick way to increase the team instead of negotiating a whole price. Say you have a team of 1 project leader, two developers and one QA and you found that you need two more developers because requirements changed, some customers just say "yes" and you are billing without too much sales and negotiation overhead.
- With agressive negotiators it's better to go to the fixed price (adding % of risk to your total).
Also when we quote by hour (indeed by days) we set a minimum budget for the project, so the customer can't reduce the project to just... three weeks, small projects can be a pain.
Because many projects we did involve reverse engineering and research we bill for that if the time required to know if a solution exists is more than 3 days and can't be solved in the pre-sales stage.