It’s more about not having to drag a cable + brick around everywhere and not needing to care about the location of the nearest power outlet, potentially for multiple days depending on usage patterns. You can instead leave the charging bits at home or the hotel and charge overnight.

This also means that battery cycles accumulate more slowly and the battery’s lifetime is stretched further.

Also, generally more efficient chips don’t get hot as easily which makes the laptop more comfortable to use and prevents fans from becoming audible unless you’re really pushing the system.