I surprised you don't envision that there must be a huge product development testbed at Apple, where they go over all these options in detail. They sold 4-6 million macs per quarter for years. They've been a product-development company ever since their inception. Sometimes it seems as if people think Phil Schiller and a summer intern are making these decisions on the basis of gut feeling.
This is like when Apple pulled back the curtain after the "Antennagate" brouhaha a few years ago, and it revealed things like a huge EM test facility, a CT scanner, etc., etc. (http://www.macworld.com/article/1152771/wireless_lab.html)
* while the mouse is precise and allows for high information density, touch requires big targets since a finger is not so precise - so Windows 10 has big targets that waste lots of space relative to a UI that is designed solely for mouse/trackpad use
* touch allows interactions like swiping, pinching, and multi-finger gestures, but because Windows 10 has to support a traditional mouse as well these are rarely used or aren't used effectively
A touchscreen does not work well with an interface that's designed primarily for use with a keyboard mouse, likewise a keyboard/mouse can't replicate all touch interactions effectively. Trying to design for both in the same UI creates a lot of compromises that will delight neither group.
I'm not so vision impaired that I need to do this on a day-to-day basis, but it's great for zooming in to see if I need to adjust a CSS border by 1px or something.
I haven't tested this thoroughly but I believe Chrome also supports the same set of touch events it does on Android. So if you want to make sure the mobile version of your site is touch-friendly, having a touch screen is less clunky than trying to emulate it with a mouse.
I discovered that I was naturally touching the buttons in dialogs and web pages and the checkboxes and radio buttons in forms. It's faster than reaching for the mouse or the trackpad. With the trablet it was the only way and it was good. No gorilla arm.
Touching links in browser can be fast too, but the target must be big enough. HN is particularly bad at that.
Basically everything that is easy to do with the touchscreen of a phone and a tablet is easy also with the screen of a laptop. But the screen must not move when you touch it.