It's just another example of the latest trend in UI/UX "experts" trying to create an "experience" for users, instead of letting the user create their own experience through customization of the UI.
People generally don't know what they want. Expecting anything but a small percentage to customize their UI, let alone even know or care that feature exists, is optimistic at best. Think outside of the HN bubble, the other 99.999% of people that use these products.
It's not the HN bubble. There are very real users who want to do small customizations to the UI. Sometimes it's as simple as, in the case of GP, this sidebar is taking up too much space and I want to reduce it. Or it can be, let me choose how I want this list view to be sorted, and remember it. Or, this button on the toolbar is for a feature I never use, and let me hide it. All of this is incredibly common in well-designed Cocoa apps, but not at all in web apps or mobile apps (including iOS-builtin apps).
Sometimes ugly is functional. Sometimes worse is better. Sometimes designers don't know what they're doing as they chase after some idealistic goal that's detached from reality.
Functional design is sometimes not good design. It's pragmatic.
This redesign is hot garbage. Take it out back and shoot it.