A social media wall displays posts pulled from a hashtag, account or location onto a screen. At events and in venues it turns the audience into the content and gives people a reason to post.
It works because it is genuinely live and genuinely theirs. Seeing your own post appear on a large screen is a stronger incentive than most prize draws, which is why hashtag participation climbs when a wall is visible.
The caveat is that you are putting content you did not write in front of your audience, under your brand. Open hashtags are hijacked reliably and quickly, sometimes maliciously and sometimes by accident, and a moderation queue is not optional: a delay of a few minutes with human approval is the minimum that survives a real event.
Also plan for silence. A wall with three posts looks worse than no wall, so have a fallback that fills the space gracefully when participation dries up, which it will between sessions and overnight.