OneDrive has a program, for Windows at least, that maintains a copy of the files in the OneDrive cloud on the local machine. Any folders not desired locally may be excluded (well, directories on the Win7 version, WIn8 is integrated wholly to the file level I think).
The folder appears identical to other folders in every way except that anything which changes, at either end is reflected soon after at the other end.
Ergo, when using 'cloud' files, there is never a need to actually operate within the browser (unless you have no office tools locally and need to use the web tools of course).
Surely Google have one too? if not, adding the ability to make the browser better for making the files seem local is something but hardly as good.
The benefits of having the files locally are many and manifest: They are an effective backup (or the cloud ones are, depending on your point of view). They are accessible faster and they are available when there is no network. They remain accessible from other devices due to their cloudiness.
Another feature of OneDrive, possible extremely useful to those away from their PC is that all the files on the PC are available via the OneDrive web page should the user enable the feature.
This is surely a no brainer. I get the requirement if you are using a Chromebook since there may well not be a local app and no local drive for a copy, not too mention the likelihood that the local space is too small for a copy of the cloud stuff.