Not sure if I'll go with this, but I did a little experimenting with 3D layering/z-depth in @broadcastsapp just to see how a real UIKit app might approach this. I think 'sparingly' is the right answer, but unlike many of Apple's platforms, there really are no physical bounds or rules to tell you not to. It’s a lot easier for a SwiftUI app to use 3D transforms and z-depth, so you'll probably see it used/abused much more in indie apps than e.g. Photoshop or Office