The answer is, you cannot answer. It depends on the context.
= is recursive assignment and := is not.
x = $(info foo) # Assign "$(info foo)" to x. Nothing will be outputted. y := $(info bar) # Assign the result of "$(info bar)", which is "", to y. So it outputs "bar" as the side effect. $(x) # Now $(info foo) is evaluated. "foo" will be outputted. $(x) # You can output "foo" twice. $(y) # y was already evaluated, so nothing will be outputted.