Earlier quoted context omitted.
I worked as Consultant for several years and instead of a daily rate, always proposed for each of my large projects, that companies would pay me 0.5% of the money my activities made the company or 0.1% of the money I saved the company. Not one ever took up on this offer...
Probably because it's ambiguous and opens them up to legal headaches when there's disagreement over how much was made or saved.
Example: Show me your current budget for your main data center. Let me show a proposal for a Cloud move that will keep equivalent or better quality of service, including training and while defining KPI's for success.