This user is trying to make a big list of the common sense (began in 2009). Oh it has taken too long...
The real problem behind the "not for extensive discussions" thing is probably that some answers on some subsites tries to appear formal and complete, while in fact, nobody knows an ideal answer. It could be still understandable on Workspace, but obviously horrible on Parenting. Answers on some other websites that nobody ever wanted a discussion usually tries to appear informal to acknowledge that "this might not be the perfect answer, but hope it has helped you a bit". On the other hand, they are more permissive to personal opinions and duplicates, instead, as a result. Alternatively, they simply don't have a commenting feature, but visible downvotes, to acknowledge that this answer is not verified by many.