It is often used to indicate something that is:
* Large in size or scope: like macroeconomics (the study of large-scale economic systems) or macromolecule (a large molecule).
* Relating to a large scale or overall view: like macroscopic (visible to the naked eye) or macro photography (photography that focuses on wide, expansive views).
* Involving a large number of elements or parts: like a macro-instruction (a complex instruction in computer programming).
Overall, "macro-" implies bigness, comprehensiveness, or a focus on the big picture.