What is the difference between Unity Answers and Unity Forums ?

Unity Forums came first, before there ever was a Unity Answers (I think.)

Unity Answers was created as a technical forum, similar to StackOverFlow. If you look at the FAQ, you can see that. Meandering Q's were ruthlessly deleted and told to post to the Forum.

But then UA got more popular, some Forum-type Qs were let slide, and even moderators decided that being helpful was more important. I feel like the Forum sort of withered, since you could almost post anything on UA (and you got points for it!!)

Then Unity Answers had a HelpRoom area added to it, which is broad enough that it really covers everything you might have in the Forum. But, there aren't really any formal rules for it, and I don't think most people really bother moving posts.

In practice, UA HelpRoom is for fixing errors or other personal Help. Forum is more for collaborative projects, or things meant to be more back-and-forth.