rkaufmann87 is correct, in my humble opinion. Following is the logic I have used in managing 3 self-built desktop towers and multiple disks (especially after disk failures):
Partitioning used to be necessary when putting very large disks in systems that could not handle the full physical disk size. But that has not been necessary for years, and certainly not for any new Mac.
Partitioning is a risky way of making things *appear* separate. It is risky because the loss of the common single-disk means the loss of all partitions. Some people think "ah ... more than one physical disk". But if all disks are in the same enclosure (MBP, desktop tower, etc) you run the risk of losing all disks at the same time still.
There is good reason to use separate storage from the boot disk:
- TimeMachine or CarbonCopyClone backups
- Easy data sharing between friends/co-workers
The disk for sharing or backup should be an external disk to prevent catatrophic loss of all disks from a single power spike or theft.
This has allowed me to recover at least reasonably gracefully from most disk failures.