Reasons to consider partitioning a hard drive:
1. Storage organization - Would you prefer a file cabinet with one massive drawer or multiple smaller drawers?
2. Defragmentation - takes less time to defragment a smaller drive.
3. Backups - easier (and requires less time) to backup a "Data" partition with your critical data than to sift through a single massive drive and decide what you really NEED to back up.
4. Operating System restoration - If you are a tinkerer who tends to fiddle with settings for their Operating System (to see what it will do) and occasionally make the wrong choice (which eventually "breaks" the Operating System), it is much less bothersome (and worrisome) when your critical data is safe on a separate partition.
5. Future plans for computer ? If you ever plan on trying to set up your computer to boot more than 1 operating system, you might as well prepare your drive now.
Partitioning and formatting a hard drive is not difficult. You use the fdisk utility to partition the drive and the format utility to format the drive.