Easier to write complex formulas, by making it possible to declare and assign values to variables inside a formula

LET(name1, exp1, [name2…], [exp2…], calculation)

exp1 is resolved and assigned to name1, exp2 is resolved and assigned to name2, then assign names to calculation for result. 

LET(x, 1, x+1) -> 2

LET(sum, total(A), n, count(A), sum/n)