Tabs are more of a navigation element. Once you are in the tab section you don't want it to be along the content. Vertical tabs share the same horizontal space with the content, its really not a great idea unless you want to grab the users attention while they are on your content.
I believe content should be wrapped with elements that compliment it further. To keep content clean I prefer to use horizontal tabs. Remember keep minimum number of tabs, its a lot easy for users to choose.
I enjoy vertical tabs. I think vertical tabs is less about reclaiming the tiny horizontal tab bar space and more about effectively using the otherwise unused space in wide screens. You basically get to see more tabs and more info about each tab without losing any more space compared to horizontal layout. Groups works quite well with vertical tabs. It basically works exactly the way it works in horizontal mode. If you haven't tried for a while, you might want to try again. TreeStyle tabs is an amazing power user feature and I really wish Microsoft implements it or at least gives the right hooks for developers to build extensions. I made this feature request a while ago [FEATURE REQUEST] Tree style tabs : MicrosoftEdge (reddit.com)
