You don't need to, however, the practice that I've always used was to break the drive into partitions based on functional organizations within your company. It is easier to identify and backup critical data that way in my opinion. Also, using drive quotas is simlified too.
For example, our Account Managers typically stored more report data and some confidential client information, so it made sense to segregate them out onto their own partition in my opinion due to the nature of the data. I set their default disk quota higher on their partition than I did the lower management.