Mirroring content/photos between devices — Tripple the iCloud backup? I own an iPhone 7+, an iPad, and most recently a new MacBook Pro&hellip;  so I'm starting to look at the more intelligent syncing of content between devices. 

If I mirror my photos (for example) or other documents between devices through iOS, does that effectively tripple the storage used in iCloud to back up that content, or is there a bit of intelligence to avoid backing up synch'd content multiple times?
No, it doesn't.  iCloud is a syncing solution.  That means it will sync everything to all devices signed-in with the same Apple ID.  

You can read more about setting up iCloud from this Apple support page.

The amount of storage will be same on all your iOS devices.  It might different on macOS because of optimized storage.  It will never be more space (or tripled).