There are plenty of reasons to own an external hard drive. Whether as a simple backup, to free up space on a full notebook drive, or for data portability between work and home, a portable hard drive is the tool of choice to offload serious data off a system hard drive. Sure, a USB flash drive on a key ring is great for convenience, but when it comes time to move hundreds of gigs of data, a mechanical hard drive can offer capacity like nothing else can.
The downside of putting sensitive data on a hard drive, and taking it out and about is that then the data is vulnerable. While Windows 8 is password protected on bootup by default, there is no such default level of protection on an external drive. Those hundreds of gigs of data, now can be accessed by anyone that finds such a drive forgotten at the local Starbucks. That external drive is now becoming somewhat less attractive.