Assume you have some web servers that run IIS with multiple webs inside. Each web is assigned to a specific IP. If you set another web within IIS to use “all unassigned” IPs, it normally won’t grab traffic sent to IPs assigned to the other webs.

However, if those other webs are stopped, then traffic sent to their IPs will get sent to a web set to use “all unassigned” IPs. I would imagine the same would hold true with webs set to use host headers.

So the moral of the story is: if you have multiple webs in IIS, be careful setting a web to use “all unassigned” IPs — it might wind up with more traffic than you bargained for.