The Android OS lacks an integrated office document viewer, something you'll come to regret over time if you are a business user. Some phone manufacturers bundle a crippled version of the Quickoffice app as a partial solution, but the functionality is pretty weak unless you purchase the $10 upgrade key that unlocks all its features.
OliveOffice is a free document viewer (.doc, .docx, .xls, .xlsx, .ppt, .pptx, .pdf, .chm) that includes a local file browser, but it also lacks key functionality that would make it really useful.
The number one reason I don't like OliveOffice is that it doesn't appear as an entry in the Save dialog when downloading files in the web browser or when previewing attachments in Gmail. These are two of the most common ways to get office files onto your Android device, and OliveOffice is no help with them.
Another problem is that some "supported" files aren't actually supported very well. OliveOffice choked on several .xls and .ppt files that I tried to open. Spreadsheets that it manages to open are read-only, I couldn't use the functions to perform calculations. Word files display fairly well, but table formatting sometimes doesn't render properly.
The ability to view compiled help manual (.chm) files is interesting. This document format is not as widely used as it once was, but it could be useful to have a help manual document on your phone, if you needed one. Perhaps if you are a tech support person, you might like this feature.
OliveOffice currently doesn't have editing capability. Other free document viewers like Documents To Go perform better, so at this point there's not much reason to bother with OliveOffice.