For example, Chrome eats pretty much all free memory keeping tabs loaded, but surrenders it gracefully when needed. That's a great use of memory.

But for an OS, and specifically for a feature that doesn't devolve unless the user goes and manually changes it, it's obnoxious. The OS is inherently a support layer for the things the user opens by choice; I'd argue any expansion of its resource footprint ought to have a clear justification.