oh i got a brainwave literally i bit of lighting struck my head and now i think i know what it means.
Ok well looking at the question with it referring to having a network drive rather then a local driver to store data files, i'm pretty sure centralised back-up is referring to that on a network everything gets backed-uptogether and there is no missing a cartain file because everyhting on everyones computer is being backed-up, but with localised that just means that only data files on your stand alone computer have been backed-up.
Well i think thats it anyway if u can understand any of it i' not even sure i can :S feel free to correct me if i'm wrong