When doing the Labs included in the Online Courses, there are questions and issues that are very specific to the proposed Lab and a dedicated forum could be helpful.
These are some of the advantages I see:
1) Efficiency: the team involved in the preparation of the labs for example, could easily answer these questions. Sometimes it's hard for beginners even to formulate the problem and ask, but when the context can be referenced things might become easier.
2) Involvement of beginners: other community folks that are doing the courses/have already done them, might also be able to answer other beginners' questions; they also know the context, they have probably faced similar issues, and they might therefore know the steps to solve it.
3) Early detection of possible errors in the labs: If there are any errors in the labs, these will be shared in the training forum. Since the specific reference to the lab will be given, this could be easily corrected or improved by the training team.
4) Other: we, beginners, will not be "pollluting" other forums with very basic questions :)
Just an idea coming from a beginner who is doing the course on "Developing Outsystems Mobile Apps".
Cheers!