Its very much subjective. What you said is not wrong, neither the one you contardict. When you have a large data model with big data size, you might want couple of calculations at the backend. For ex. your requirement says that you have a sparsely populated(data for discrete dates) data set and you need to show the report as continous, in that case you might want to populate the data for the missing dates at the script, rather than calculating it at the front end everytime users select a POV, because that would make your front end performance fall significantly.
Hope this gives an idea.
