I need access to an "Office-like" suite on iOS
If you don't need 100 percent Office compatibility and only rarely need to create/edit Office-like documents on your iOS device, then there are any number of better options than Microsoft's subscription plan. The aforementioned iWork for iOS apps may be all you need, given they can output Office-compatible file formats when required.
If you don't need the full suite, there are also individual apps out there for presentations, text editing, and spreadsheets, any one of which may meet your needs. (If only the App Store had a "try before you buy" plan, you could test them to see which worked the best. But they don't, which is why I recommend buying apps that also offer traditional free trials via their developer's websites.)
So much for the clear-cut buckets; this next one is the most complicated, even though it seems simple at first.
I use Office at home, but never on iOS devices
Given you have no interest in Office on your iOS devices, you may think there's no reason to sign up for Office 365. And that may be true—but it may also be false. It really depends on how many computers you have in your household, and how often you refresh your Office installation.
I use Office at home on just one Mac
If you're just one person, working on one Mac, then things are pretty simple: there's no need for Office 365, even if you upgrade Office each time there's a major release. Office 2011 for Mac is $140, or $220 if you need Outlook. (These same prices apply to the Home and Business versions of Office for Windows.)
On the Mac side, at least, Office isn't updated all that often: Office 2011 was released in October of 2010. Assuming a new release comes out in 2014 (and you want to upgrade to the latest version), you could expect to use it for at least the next three years, for all of $140. Compare that to the $300-plus you'd pay for the subscription over those three-ish years, and there's absolutely no reason to subscribe; just keep using the standalone version.
I use Office at home on multiple Macs
Things get murkier when you add multiple computers to the mix, because of Microsoft's licensing: Office is only sold with single-machine licenses. If you have two Macs, your upfront cost is now $280. That makes the three-year $300 subscription cost comparison a lot closer to break even. What if you're married, and/or have kids, and they have a computer or two? Now you're up to four computers, and a $560 up front cost. With three or four computers, the decision on whether to subscribe or not is no longer black and white.
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