[mythmon_]

Since on most platforms the tabs go all the way to top of the window now, there isn't room to grab the window to move it around. Those spaces act as extra drag targets.

[manaskarekar]

On many linux distros, you can grab any window and move it around by: 'Alt + Left Click' anywhere on the window.

Bonus: You can resize any window on these same distros by 'Alt + Right Click'. It will allow you to resize along the closest border(s).

[minedwiz]

You mean those spaces are on purpose?

[kuschku]

Correct, if you maximize the window, there’s otherwise no way to drag it back down without clicking on the maximize button.

As many users rely on the functionality, they had to be added back.

You can configure them in Customize → Drag Space (on/off)

[minedwiz]

Interesting. Cool about the setting.