Andy Leonard shares some thoughts:
Right-sizing didn’t always work out the way some clients were led to believe it would.
In nearly every instance, the right-sizing argument was presented (sold) as the solution to over-provisioning, or purchasing hardware to serve peak loads. The classic example was a US income tax service that needed more and faster compute available to meet increasing demand starting in late January and peaking in mid-April each calendar year. After mid-April, hardware that was beefy enough to handle that peak load sat mostly idle for the next 9 months.
I don’t think I’ve ever worked for a company where this scenario really made sense. Even in the e-commerce company where a sizable fraction of our total annual revenues happened over a 5-day period, the load was still significant enough the rest of the year that we made good use of our on-premises SQL Server hardware.