Do we really need the Iterator SUMX in this case?

We have been told up to this class ("DIVIDE") that the "Iterator SUMX" that has been mimicking the "Total Sales Amount" and that now we would understand its necessity. However it is not the case.It is the DENOMINATOR which makes the difference in seeing the desirable result, not the NOMINATOR. If we write the code in the following way, we will still get the desired result.

% Sales Amount Selected Age Bucket = DIVIDE([Total Sales Amount], CALCULATE([Total Sales Amount], ALL(dimCustomer[Age Buckets]))).

Other than the expectation on finding an use for the iterator, the content is great. But it still makes me wonder about better use for iterators. Am I wrong or is just my head exploding over hours of study?
=D

Many thanks!!!