OTOH, with horizontal tabs, once you’ve reached a certain number of tabs, they all condense into indistinguishable icons, and even before they have, you can easily only see a couple of the tabs entire titles at a time (on a laptop screen).
So even if you don’t manage tens or hundreds of tabs (although many others do), vertical tabs are still useful because they allow you to never have to think about closing a tab, and still have a great experience with the 5-10 tabs you are interested in at any one point of time.
That's Firefox, and while I've got plenty of extensions, none are affecting my tab behaviour.
Some people seem to strongly prefer Chrome's behavior. The only advantage I can see is that it forcibly prevents your tab count from getting out of hand.