As you surmised, if a macro is only gonna be called once there's little benefit, outside of possibly letting other mods that interface with your mod call the macro.
The only real benefit would be to avoid variable poisoning. Essentially, if you have a macro, it's like calling a function in PHP (and that's largely what happens when the template is compiled, but I digress); variables defined inside a macro do not affect the HTML surrounding it.
How useful that would be to you, that's another matter entirely.
Fillip