Currently, only UK JustGiving users have access to this feature. Allowing this feature for the US clients will create campaign previews on the main charity landing page. If added, donors visiting your charity page would be able to see your current campaigns requesting funding, in addition to the general donate button. There is no feature right now where a donor can see all the campaigns a charity has open for donations. If added to the charity landing page, this could all be viewed in a central location, versus having to share the specific campaign URLs.
Here is an example from a UK client of a campaign being featured on the main charity landing page: https://www.justgiving.com/actionforchildren
You can see "The Giant Wiggle 2017" highlighted in a box, showing their goal and how much has been raised.