Invision Community allows the ability for guests to create a response to a content item they wish to engage with, without barriers of first creating an account, by allowing the user to post and then register afterwards.
This will be incredibly valuable when you consider how much traffic a forum receives from inbound Google searches. With Post Before Registering, you'll increase your chances of turning that inbound lead into a registered member contributing to your site.
You can switch on posting before registration in the following location within your admin CP.
System -> Settings -> Posting -> General
When a potential member posts a new content item, or responds to an existing content item, they will be asked nothing more than their email address when posting, as seen below
Once they have posted, they are asked to simply complete their registration. They are more likely to do this now they have invested in your community.
Therefore guests will see the ability to submit content, but then will immediately be prompted to register an account before the content is actually submitted and viewable. This is useful for encouraging guests to register.
Guest users will have up to one week to complete their registration before their content will be permanently removed. If the guest user does not complete their registration immediately, they will be sent a reminder email shortly after making the post.