It is a very, very easy way to build document-centric internal applications for enterprises that use .DOC and .XLS files (meaning, every enterprise). It's popular for exactly the same reason Access was popular: it drastically reduces the cost of basic business applications.
Normal everyday people don't get much direct benefit from it, although they do benefit indirectly:
* They don't have to implement business processes by "mailing form 3021-C to Clara in Purchasing"
* It sets a lowest common denominator for bizapps that is better than what enterprises get from bespoke .NET and J2EE dev.
You work for a large company with IT locked down, and this is the one "collaboration platform" available to you. Oh, but no Sharepoint Designer for you, my friend, if you want to make it do real tricks it will be with emacs (assuming you have jumped through the nine rings of fire to obtain permission for cygwin).
If you work in an environment that makes heavy use of Microsoft technologies (specifically, Office features), then it makes doing collaborative stuff with them easier. Its value depends on how much you buy into that.
What is the benefit/value prop to a normal everyday person and why would they use it/love it?