What problems is Stack Overflow Internal solving and how is that benefiting you?
It starts by helping the team communicate in an effective maner to solve technical problems on a daily basis. The people with the actual knowledge use the tag system to keep an eye on new questions that require their expertise.
Once a problem is posted as a question and an answer is made to that question, the entire team have access to that information and all the team, including the new members will benefit for the rest of the life from the _expert_ knowledge posted in the answer.
The Wiki format allows the posters, but also other members of the team to further refine the question and the answer(s) to that question, so you can have not only the general knowledge, but very specific solutions to very specific problems. Review collected by and hosted on G2.com.