It appeared in a semi-recent update and I can’t find any documentation about it. I’ve experimented and it doesn’t seem to do anything to the bar. I’ve also searched the available documentation, plus release notes, but see no mention of it.
Is it perhaps intended to replace the old Outer Spacing setting that used to be in bars but is no longer available?
I ask because with the outer spacing removed my old headers have broken (or more specifically, their elements now touch the left and right edges of the browser window if the window is sized equivalent to a portrait oriented tablet) and I’m having to retrofit dozens of sites to avoid this. Currently I’ve been going in, changing the header height to auto then adding padding to the bar, but I’m hoping there is an even easier way with less clicks.