Is there data or research on the tradeoffs associated with allowing anonymous posting on forums like Piazza? A large amount of research from the EdTech world finds that forums that encourage social learning, if used right, can significantly improve learning outcomes. Of course, there are downsides. 

One of the main platforms that I've seen across universities here in the US, is Piazza. 

Piazza can be configured to allow students to post questions, answers and comments completely anonymously. There are classes where this works very well, participation rates are high and spam is rare. However, many faculty members, some because of unpleasant interactions in the past, often disallow anonymous posting.

Is there any research/anecdotal evidence that suggests anonymity hinders / helps learning? In the latter case, are there specific steps used on anonymous fora that are required to maintain quality? We're planning on building a large QA-system within our EdTech platform, and on the fence about investing thousands of dollars to build "anonymous posting" within our system.
I have used Piazza in many mathematics courses. I can say, anecdotally but confidently, that students LOVE the anonymity option. Not everyone uses it, but I have had plenty of them tell me, either in person or (anonymously!) on course evaluations, that they appreciate the option since they can ask a seemingly "dumb" question without fear of appearing ignorant or uninformed. Perhaps this is particularly relevant in mathematics, where anxiety and performance-based fear is, alas, quite normal, but I'd imagine students in other disciplines would make similar comments.