I’m not the parent commenter, and I don’t use it, but if you have a lot of tabs, it’s easier to navigate between them in a vertical list if you are used to looking at the tab titles to decide which one you need.
This is partly because the tab items get very narrow when there is a lot, but also because in a vertical list there’s just a lot more room for them. The top bar is ok when you know the tab you need by it’s shortened title or position, but a vertical list is better when you don’t and you need to search for it by it’s full title or when it’s further away.

Maybe I should use it too.