Craig Federighi:

And if you look at the window title bar, you’ll see how the use of translucent material gives you a sense of place as you scroll your content. 

Now, these same carefully crafted translucent materials are used in the sidebars. So now, your windows take on the personality of your desktop. As you change your desktop picture, your window adapts to reflect that personality and that temperature.

And that translucency helps retain a sense of depth and place as you move your windows over one another.

The above is not a quote about Liquid Glass. This is Apple’s VP talking about OS X Yosemite, way back at WWDC 2014. 

It’s curious to see the similarities to what Apple unleashed last week. Honestly, though, these were the design aspects of Yosemite that I least liked at the time, and they aren’t things I’ve grown any fonder of over the years – especially on the Mac.

It is notable, however, that Federighi uses the term “carefully crafted”. And the translucency was relatively subtle in Yosemite. For me, much of the problem with Liquid Glass stems from how overbearing it is: as I said in my piece for WIRED, rather than helping you focus your attention on what you’re doing, it demands attention for itself.