I'd like to have a server dedicated to staging sites in my cluster which means we would have a staging Role available.
It would help not to expose our main application server IPs where live websites are running. It may also help SEO not to run live and staging websites on the same IP.
Some customers also forget to delete their staging websites and these sites are sometimes super messy, heavy and not updated/taken care of. It eats the resources of critical live websites.