The best reason I can think of for having cad standards is that you can automate so much more of your drawing process if you have consistency in layering, linetypes, colors, locations etc.
The last job I held, we had very exacting standards, from the exact location of dimensions in relation to a part, to the layers, to the location of the drawing on the sheet. The development of these standards took nearly 10 years, and by the time they I left their employ, what had taken 7 to 10 days to design, could be done completely and accurately in 4 hours.