What are the benefits of a partitioned hard drive, or some practical uses of a partition?

Disk partitioning is one of those things where you find many conflicting opinions. Some will swear that proper partitioning aids performance, makes backing up easier and is just generally "better".
Others just opt to let Windows sort it all out, believing that improper partitioning might well prevent the file system - already optimized for both safety and performance - from operating in a maximally optimal way.
The truth is somewhere inbetween; I'm certain.
While I tend to fall into the latter camp, I'll look at some of the pros and cons to partitioning your hard drive, and make a recommendation if after all is said and done you're still not sure.

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A partition is nothing more than a way to organize the physical space on a hard drive. We typically think of a hard drive as a single disk, but partitioning allows you to split a hard drive into appearing as multiple, different drives. It's still the same single disk in hardware, but the space on it is divided up and appears as two or more drives in Windows.

"A partition is nothing more than a way to organize the physical space on a hard drive."

There are two classic approaches to partitioning a single drive on a Windows PC:

• Single partition. Typically, your computer has a "C:" drive and all of your programs, data and operating system files are contained within it.
  
• Two (or more) partitions. You hard disk is divided into two or more partitions. "C:" remains, and typically contains at least the operating system and often installed programs, but additional drives - perhaps "D:", "E:" or others, also exist and are then used for data storage.
  

Why might you partition?
There are several reasons you might consider partitioning your hard drive:

• Organization: some people feel that splitting data or components across multiple "drives" is a better way to organize their data than creating more folders on a single drive.
  
• Backup: specifically, backup granularity. It's easier to backup entire partitions separately. Say your operating system is on drive C: and your data is all on drive D:. If you ever need to reinstall or revert to a backup it's possible, depending on the situation you're recovering from, that only drive C: would need be affected, leaving your data on D: untouched.
  
• Security: whole-drive encryption is often really "whole partition" encryption. Thus with multiple partitions you could pick and choose which might be encrypted (typically a single partition containing your sensitive data.
  
• Speed: Depending on how you use your data, it's possible that moving less-frequently used data to a separate partition "out of the way" of the data you use frequently can have a speed improvement.
  
• Multi-boot: if you want to have multiple operating systems installed on your computer that you select at boot time, each must reside in a separate partition. It's also common to create an additional data partition that they all then use.
  

Why might you not partition?
Again, there are several possible reasons:

• Drive Letters: each partition is typically assigned a separate drive letter. While there are some ways around this, letters can quickly become a scarce resource for machines that are heavily network connected, have multiple memory card slots or CD/DVD readers, or use software that also requires drive letter allocation.
  
• Backup: more specifically, backup oversight. If you have multiple partitions it's either more work to make sure that they're all being backed up properly, or it's easy to miss it.
  
• Speed: Once again depending on how you use your data, it's possible that by having data on separate partitions your hard disk will have to work harder to access data that's spread out further apart on the media.
  
• False Security: even though separate partitions look like separate drives to Windows, they are not. What that means is that if the physical hard drive holding those partitions fails, all the partitions go with it. While you might be applying different backup criteria to different partitions, the fact is that underneath it all they share several common risks.
  

Once again the "should I or shouldn't I?" question gets my most common answer: "it depends". It depends on you, your data, how you use your computer, and even to some degree the hardware configuration of your computer.
My Recommendation
Unless you have a specific reason to partition, don't bother. Instead:

• Use the NTFS file system - which does a pretty good job of optimizing for speed, space and reliability, and won't restrict the size of your partition.
  
• Defragment periodically. Weekly if you're a heavy user, monthly if not. Much of the performance gain you might get from separate partitions is very similar to simply having a defragged hard disk.
  
• Backup everything regularly. Having separate partitions doesn't remove the need to backup, it only changes how by making it slightly more complex.
  
• Use folders to organize your data. This is what folders are for, and they're significantly more flexible than separate partitions.
  

If you do have a specific reason, then by all means go for it. Don't forget that it's still a single hard drive you're using, and that all your partitions need to be properly maintained and backed up.