TL;DR Wikis are awesome tools. When used poorly, they’re like black holes; documents disappear into the ether. When used intelligently, they can be powerful, self-organizing knowledge centers for your team.
On most large software projects, organization is key. Developers aren’t always the most organized people in the world (I’m no exception) and project managers tend to focus on the project schedule. This can leave something to be desired or tracking the team’s progress and keeping everyone on the same page in terms of technical decisions and understanding of the larger system architecture as the project progresses.
Most projects hit a speed bump or two along the way, and it isn’t uncommon to have people scrambling trying to remember what was agreed to and when or struggle to remember why or how a certain decision was made.