As for the ones asking why run more than one 3ds Max instance? Here's one that applies to me:
Example I'm working on a project and I need a new material/shader, let's say for instance for some type of wood. I open a new 3ds Max with my material testing scene. I create my material, I render it out on my material ball and I save it in a mat file, and I add it to (in my case) Connecter. So when done, I can drag it over to my other Max instance that has my project open and apply it or I can easily find it again for when I need it in other projects.
I'm NOT going to close my project, open my material scene, create the material, close that max file, reopen my project apply the material, only to discover 5 minutes later that I need another material, or that I need to tweak some things in the original material that I missed first. This is wasting a LOT of time on closing and re-opening.
Having another Max instance open to prepare materials, assets, in testing scenes specifically designed to do just that, has proven to be an extremely valuable time saver, either for re-use but also for consistency in look and quality.
What about Xrefs (scenes, objects), containers and whatnot. Are you guys telling me you're closing and reopening your projects every step of the way? Then you're literally spending half your time on that. I'm sorry but I like to work fast, and so do my clients.
Having another Max instance open to copy from one project to another (indeed that's why there are so many copy paste scripts, god forbid this is a standard functionality by the way) is also something that is used a lot. No person (in their right mind) that likes to work fast and organized should work in one 3ds Max instance. It's. Just. Not. Feasible.
I have another theory that would make this ordeal understandable. Maybe Intel payed a lot of money to Autodesk to make sure that AMD's flagship processors barely work with their software, so when time comes we switch back over to Intel, I know I am starting to yield. Seems far-fetched? Maybe, but it would explain to me why the **** no-one's doing anything about it.