There is the excellent HTML help system already, so what extra value can a Wiki approach take?
I would suggest - a lot.
Here is the "official" help portal: file:///<lazarus_installdir>/lazarus/docs/index.html which is the canonical resource - and always up-to-date, but it is not task-oriented, and example source code is not always available.
The "Tools/Example Projects" is also a mine of coding information.
Beginners like example code to both get a kick-start and also learn the language by example, and for that, the Wiki is a useful and accessible resource.
The downside is of course, lax maintenance of the Wiki.
I started the Wiki category "Code Snippets" purely for my own benefit - often I would follow a forum topic and come across a really good solution which I thought could be lost among the static.
All I had to do was copy/paste the code into a new wiki page, and add "Category:Code Snippets" but being a typical programmer I got lazy and stopped after a while.
This new initiative looks like a real step forwards.