This is probably the most common use of wikis. Projects or labs often have have a variety of project documents; announcements, to-do lists, status summarizes of various subprojects, documentation, meeting agendas, or hints and resources for others in the project.
Without wikis, nothing on a project site can be updated without the webmaster.
The result is often stale, out-of-date websites, and the real business shifts to email lists. By allowing project documents to be jointly maintained by the whole group, wikis remove the webmaster bottleneck.
This sort of wiki is often access-restricted (or edit-restricted) to those in the group.