Some people strongly prefer to have an external battery that can be swapped (as in pull a tab, remove the battery, and plug in another, which is fully charged). Older Thinkpads (T480 and earlier) had a second, smaller, battery inside that would keep the laptop running while the main (external) battery is being replaced.

I've been using various Thinkpads for 10+ years and have yet to use this feature. But hey, to each his own :)

Yes, I also prefer the 2nd external battery on my T470.

But in today's market it's still one of the most simple to change batteries. And you know you can still purchase a genuine one, 4 years later for a reasonable price