Ideally, if the macro is for use in this document only it is in the document. If it is for use on similar documents, it is in the document template. If it for use only on your computer and for many different kinds of documents it might be in your normal template. I would definitely store it in a different Global Template though if I wanted to share this common macro.

I would have to both trust and like someone a whole lot before I would substitute a normal template that person sent me for the one already on my computer. Doing so would disrupt my regular work. There are lots better places to store macros.

I would strongly suggest you take a look at Distributing macros to other users for ideas before you get someone mad at you.