Illustrator should support both ways: 1) global scale for the whole Document, and 2) assigned for each Layer. There are scenarios when you work only with one scale, so not to complicate the process, a global scale is handy. Let's say you have an elevation of the building, and you need to create a mural on one of the walls. You select one scale for the whole Document, and that's it. There are scenarios when you need to work with multiple scales in the same Document; in this case, scales assigned to each Layer are helpful. Say you need to show the mural on the whole building elevation and show the enlarged mural right next to it. !!!!!!!!ALSO!!!!!!!!! Scales should not be adjusted only when creating a New Document. This should be flexible and editable at any time. CADTools came up with a brilliant solution that has worked for decades for so many people. Use the same logic but make it a native feature. As collateral, this will make the new native Dimension tool usable.

@Egor – We're talking about an option to scale the artboards when creating a new document. Example scenario... I'm designing a Wall wrap design that when installed will cover a 20 ft x 8 ft wall. Because of the intensity of the design and software not running well at those larger sizes and high resolutions, I know that my art can be setup at 1/4 size for the printer. It would be great if I could go into illustrator when creating the document, and say it's going to be 20 x 8, and then hit a scale dropdown and select 1/4 scale. This would make the artboard 5 ft x 2 ft, with some sort of notation in the file that the intended final size is 20 x 8.

Dan and others — do you really mean scale should be allowed to set only on a document creation?
And do you really need it to be set per document? Perhaps, it should be set for a layer? or an artboard? or a group?
How do you expect to access and modify the scale value? Please elaborate.

Yes, need this. I do corporate interiors and have to create scaled templates all the time from the architectural elevations. Could also be a feature that is added to a layer.
Let's say you import a pdf of wall elevations drawn at a 1:64 scale. If I could create a 1:64 scale layer, and then draw on that, it would be very helpful.

This! Yes Please!!!

As a designer of signage, of many sizes, I can’t tell you how valuable this would be. It is common industry practice to be forced to deploy a competitor’s platform as well as Adobe’s, to facilitate “document level” scaling. This serves to remove the human error inherent in making scaling adjustments manually within the documents’ individual elements. This would help many math-challenged creatives (a common critter) leap the scaling hurdle and be both more confident and productive.

My additional wish is to have a companion export function that converts elements to full size while also flipping to common manufacturing machine input formats. We’d pay for that kind of manufacturing specific extension...

I vote for this too! Also, the ability while in these scales to be able to select an object within the document and see it's scaled size information.

I'm also looking for this feature. It would eliminate calculation errors and make the life of the designer much easier. I would like it if you could choose to design @ 10%, 20% or 50% of the actual size.