In this tip, Edward Owen explains how he deals with bloated scale lists in AutoCAD.

"Once in a while, we get drawings that are so bloated with extra viewport scales, it's next to impossible to reset or clean out the list. Even trying to change the scale doesn't always work. Typing in ScaleListEdit brings up a dialog box to help alleviate this issue, yet it doesn't always work. If you've tried this method and it generates an error, try typing - ScaleListEdit (add a hyphen before the command). This will bring up the Command line prompt. At the prompt, type in R for Reset, and the list will clean itself up. Works like a charm!"
 
Notes from Cadalyst Tip Patrol: Scale lists define which scales your file can apply to annotated objects. In AutoCAD versions since 2008, you can make text, dimensions, hatch, and blocks annotated. That means that if they are in model space, they can be displayed at a specific size in a viewport, according to scale. This list controls what scales can be applied. With this feature, users can define an annotate text style to display at a particular size when printed, regardless of the viewport scale. If you label something in model space you would have to scale the text to be visible in a viewport, but it would only work for one scale. Define the display size and apply scales from this list — or just label it in paper space.