In the simplest case—Asturian for example, which was only printed once—Translation ≡ Macroedition ≡ Edition: the three sets are equivalent to each other. The case we most often think about is Translation ≡ Macroedition but there are multiple editions: hardcover, softcover, anniversary editions, house editions, illustrated editions... all those books that fundamentally have the same text. In both of these cases, a 'macroedition' is superfluous and it doesn't help us.
It is possible to just say "English" and not distinguish between any of the English editions of the books—but we know that the American English text and the UK English text are not the same and intuitively we want collect them into their own sets. Similarly, we want to capture the set of editions that are the original Italian translation vs. the newly revised Italian text, both of which have muliple editions each. We want to capture Braille editions as distinct from their counterparts; we want to capture audiobooks as distinct from the text they are narrated from.
These are the variations that 'macroeditions' capture: regional adaptations, significant revisions of the text, transliterations into other writing systems, modality shifts (print to audio). Think of it this way: the first edition of a translation is published—that's the simplest Asturian case—we categorize that 'macroedition' as a translation (Tr) in recognition of the fact that at that point, 'translation' is equivalent to 'macroedition' as sets. If and when a new edition gets published that is distinct along any of the relevant criteria, we create a new 'macroedition' categorized appropriately.
The term is not entirely without precendence—it was inspired by 'macrolanguage' which is the term linguists use to refer to a group of languages that need to be refered to collectively for some reason: 'Chinese' is a macrolanguage that includes many non-mutually intelligible languages united by a common writing system. Similarly 'Arabic' is a collection of now quite distinct spoken varieties united by a common literary language. Serbocroatian is macrolanguage that refers to language spoken by individuals that self-identify as speaking different languages due to sociopolitical factors. Similarly a 'macroedition' affords us the ability to accurately label and conveniently talk about sets editions that share certain characteristics.