So in Advanced Warfare when you look at a weapons stats the last one is mobility. You will see a boot next to it. Im sure like me you thought that had to do with how quick you move when carrying this weapon. The sad truth is that is just wrong. Mobility is how quick you ADS ( Aim Down Sights ). For most weapons each point of mobility is equal to 1 less video frame. This holds true for everything but Heavy weapons they get 2 frames for each point.
All in all this stat / modification means nothing. You really gain no advantage.
I have attached a link to a video by Drift0r. He dose a great job breaking it all down for you. If you have 3 and a half mins take a look.