You should always have a macro in your kit, and with the new Irix 150mm macro, owning that lens becomes easier than ever before.
A macro lens lets you get a very, very close up shot of something. While long lenses, like a normal non-macro 135mm prime, are wonderful, they often have far out close focus distances (on some anamorphic lenses, as far away as 6 feet!) that make it hard to get that “just the iris of an eye” shot you are looking for.
A macro lens lets you get that tight insert on an eye, a pencil tip on paper, or any other detail of the scene that is going to help you tell your story and make your editor’s life easier in post. Every job I do I am sure to make sure there is a macro somewhere in the kit—often the beautiful but very-expensive-even-as-a-rental ARRI macro, and there have even been a few jobs I’ve done that shot only on macro.
Source: No Film School