Nick Simons from the Office Web Apps teams shares why he prefers storing documents on Office Web Apps (SharePoint and Windows Live SkyDrive) even though he has Microsoft Office on the desktop:
1. When I need to get people’s feedback on something I’ve written in Word, I just put a link to the document in Word Web App viewer. I don’t need to worry about what version of Word other people have. It doesn’t matter if they have Word at all. They will be able to view my document as long as they have any of the more commonly used web browsers. And when someone uses the viewer, there is no risk that they might accidentally open the file and prevent me from editing it.
2. If I am using a machine that doesn’t have Office installed (maybe a netbook, an internet kiosk, or just a machine I haven’t finished setting up yet) I can still get to my files to view and edit them.
3. This really isn’t a feature of Office Web Apps but I use multiple machines in multiple locations and I can always get to my files. Not only that, but when I open files from SharePoint or from SkyDrive they open in the desktop apps seamlessly. That is, when I click "Open in Word" the document opens in Word on the desktop exactly as if the file were local. This means that any changes I make are written to the file on the server. Even better, if for some reason the server becomes unavailable Word is smart enough to keep a local version ready to automatically synch to the server when it becomes available again.