A single step up for a single DB can cost from 10% to 25% more than the previous sizing, which translates in 15K or more when dealing with higher specs databases; remember that this is for a single scale up, on a single DB, on a single year.
It’s easy to understand that if your database and/or queries are not well tuned because “scaling will take care of it eventually”, then, you’ll be secretly bleeding money.
We can quantify performance improvements in terms of resource savings, but tying that to the specific business benefits can be hard because that hardware is a capital expenditure and so much of tuning benefits are “we avoided this worse case” rather than “we actively scaled something down.”