I have no idea why anybody would try and mix by audio suiting eq's.
Aside from the exceptions Henchman mentions in the same comment,
- because it's a dicey change and you want to make sure it'll work while you're editing, before ever doing an automation pass
- because you might be passing the project to someone who doesn't have exactly the same plug-ins
- because you'll be archiving the project, and might have to make changes in the future after you've changed or upgraded your system, or after a certain plugin has been abandoned and died because of an OS change
- because you're working in Nuendo
or some other DAW that renders faster than realtime, and you want to do something that takes realtime or longer to process. (Okay, it won't be called audiosuite in the other DAW, but the function would be the same.)