Array Formulas have been around since the beginning of Excel. The author wrote a whole book about them back in 2012. Array Formulas were powerful, but complicated. Then Microsoft invented the new Worksheet Calculation Engine in Microsoft 365 Excel and just like that, 40 years of Excel worksheet formula methods changed overnight. Dynamic Spilled Array Formulas, born inside this new calc engine, can now spill results from a single cell and dynamically update when new source data changes. Now we don' t have to lock most cell references; no need to manually copy most formulas, editing formulas is now a simple task, and insane old school filtering, sorting and unique list formulas are a thing of the past with new Array Functions like FILTER, SORT and UNIQUE. Microsoft also gave us the LET function which eliminates duplicate formula elements by allowing us to define variables within the formula itself. In addition, Microsoft gave us the LAMBDA function which allows us to define re-usable functions without using VBA code. There are also LAMBDA Helper Functions like BYROW which solves the problem of " how do I spill an aggregate total?" Does all this sound too good to be TRUE? Too good is no