While learning stack allocation, I came across this paragraph in the textbook (Programming Language Pragmatics - 3rd Edition):
Even in a language without recursion, it can be advantageous to use a stack for local variables, rather than allocating them statically. In most programs the pattern of potential calls among subroutines does not permit all of those subroutines to be active at the same time. As a result, the total space needed for local variables of currently active subroutines is seldom as large as the total space across all subroutines, active or not. A stack may therefore require substantially less memory at run time than would be required for static allocation.
I would appreciate if anyone could explain how stack allocation would save memory when used for allocating local variables. I tried reading this many times. But I can't understand the author meant.