Is there a list "Why should I put stuff into the same region"? I understand that people might want to

You list is a good start. The other main reason I can think of would be to allow applying a single clustering config, e.g., to a group of cached things (region). This is something that is not possible today, at least in hibernate-infinispan IIUC, because there is no well-defined mapping between region-name/cacheable-name to "cache config" (or "template" I think you call it?). I discussed this above[1] as something I'd like to see a consensus on across cache providers: a sort-of fallback approach to how a "cache template" is resolved

[1] https://hibernate.atlassian.net/browse/HHH-11356?focusedCommentId=90111&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-90111