You won’t create new formulas in your cube very often. New formulas are usually a staple of building a new cube, but beyond that it isn’t a typical task - and remembering how all the different formula types function across your dimensions (i.e., at leaf levels vs. a parent level) isn’t exactly like riding a bike.
Our Product Adoption Team developed this amazing cheat sheet to explain how the different formula types and time conversions function with your account type dimension.