For me, it's because I like to have my program files on a separate partition from my games. My games are all on one partition
I`m just curious, Why do this? Does it improve performance? I guess if the hard drive was partioned into smaller sections the pc could access files faster, I think.
It can improve performance, reduce defrag and backup times, and improve chances of recovery from disk error, data loss, or loss of a volume - since all your eggs aren't in just one basket. Drive failures, disk sector damage, and user error occur. Partitioning can help mitigate the damage, speed recovery, and minimize loss of data. I know this from personal experience.
I maintain separate partitions for:
* the operating system
* program data and user profiles
* system pagefile
* archives (usually patches and updates, as well as progams that I download and wish to retain the installers for)
* temp stuff (where my browser downloads go by default - like programs/apps I want to try out, game demos, etc.) that I may install or open once or twice then uninstall or delete.
Operating system, program and archives don't change much. Defragmentation times are reduced on those partitions, and when I do a backup, I usually skip those partitions - because I have disks or can re-download what is needed to recover.
program data and user profiles change moment to moment. I back these up more regularly, and defrag these partitions more often. But both processes take less time and money (in terms of storage costs) than doing full backups or defragmenting all four drives (which total about 660GB on my main home PC).
I never backup or defrag the pagefile partition or temp stuff. A fault on those partitions is completely recoverable.
If you get fancy and put your operating system, pagefile, programs and data on different spindles (drives) you can maximize read and write performance (and thus, overall system performance) as those operations run through separate disk controllers and bus paths.
Bottom line: Maintenance time/costs, risk of data loss, and disk operation times, are all increased on a system with a single partition that contains everything.