Richard Fahey, writing about using wikis for gathering requirements on the SAP Community Network:

Documents need to ‘live’ throughout a project; their usefulness should not end once the project phase has been completed. Having information on a wiki allows it to be easily edited and updated thoughout a project. Modifying Word documents requires updating versions, tracking changes, emailing the latest versions etc. Within a wiki, the software handles all of this, and as such it’s a more productive medium for living documents.