For new feature junkies and security minded
Subscription software means you will always be able to update to the latest and greatest version of Office. As with previous versions of Office, you'll get the latest security patches, an important feature considering Microsoft in December warned that hackers are turning their attention to uncovering Office exploits.
Beyond security updates, however, you'll also get new features that come out. And if a brand new version of Office is introduced in another three years, you'll get to upgrade as part of your subscription.
I just use Word and Excel on my desktop
Here is some simple math for those who are not Office power users with one PC. For one PC, Office 365 is $100 per year. For one PC, Office Home and Student is $140. You can use Office Home and Student for as many years as you like. You'll do fine with a boxed version of Office 2013.
If you're still on the rental fence
Like any subscription product, your ability to use the service is tied to your yearly subscription fee. If you stop paying, your Office software goes away. You'll still have all your documents on SkyDrive or your local hard drive, of course, but you won't be able to use the editing features in Office once your subscription runs out.
If you prefer to own your software or don't think you'll be willing to maintain an Office 365 subscription long term, then the boxed version of Office 2013 might be for you. The downside is when Microsoft moves to the next version of Office in a few years, you won't have the latest and greatest version like Office 365 users will.
For cross platform mobile warriors looking for a mobile Office solution
Along with your new Office 365 subscription, Microsoft would really like it if you used Windows Phone for accessing Office on a mobile device. But the reality is most of us are using either an iPhone or an Android device for our smartphone and tablet needs. That means when it comes to editing Office documents on these platforms you have to find an alternative to Office. That's not such a huge deal on iOS since Apple's iWork package is available, and there are alternatives on Android as well.
Microsoft has yet to announce versions of Office for Android and iOS, but there are persistent rumors saying mobile versions of Office are in the works. It's not clear, however, if Microsoft would release Office for iOS and Android, or just for Apple's platform.
Office 365 is a novel way to use Office and some of the free perks, including those Skype minutes, are a nice addition. But paying for Office every year might take some getting used to for anyone tied to the traditional desktop software model.