The host filter at the top of each page in DPM should provide a list of the possible tags for filtering hosts. This was an ability that existed prior to the most recent host filter changes (which expanded the available syntax for host filtering).
Customers can apply arbitrary hosts to tags, but there is nowhere in the app that displays a list of tags (except for scrolling through the entire list of hosts). This is problematic for clients with many dozens or hundreds of hosts, which might have any number of tags applied to them, which may have been applied by other team members or algorithmically.