While there might be issues with Office 365's reliability (I don't know, I use Google Docs), the online collaborative capabilities is a fantastic tradeoff. Mailing individual files amongst a group of collaborators impede productivity (even though it has other benefits).
You could make the argument that cloud solutions are not a prerequisite for collaborative tools like Office 365 or Google Docs, but desktop peer-to-peer systems like those that Groove Networks (https://en.wikipedia.org/wiki/Groove_Networks) tried to create did not take off.