[iamtedd]

6. It's the only alternative if you want to keep UI elements out of your title bar.

[oblio]

7. Vertical tabs can easily have nesting (subtrees), just like those file manager left hand side windows. So you can structure your tabs better.

[amelius]

Theoretically also possible with horizontal tabs.

[oblio]

But not as scalable. You either have a very wide horizontal ribbon which needs a lot of side scrolling, or a shallow depth that doesn't allow you to group as much.

There's a reason every tree/file explorer in existence is vertical :-)