It's like we tell the kids: sharing is caring. Which is all well and good until the time for your event comes and you didn't realize you were supposed to share with another event!
There are notifications on the event page to let you know what's being shared, but to add some additional visibility you'll now get an email as well. It will let you know that your event is sharing rooms and/or resources with another event, as well as the resolver's reasoning for making this call.
It will look a little something like this:
Sharing is caring and communication is key, now go play nice with each other!