Comment 10 for bug 1165173

Android apps are already using "overlay thumb/handle scrollbars" or "fastscroll" for faster and/or more precise scrolling, including the most popular apps like "Whatsapp".

Examples:

https://code.google.com/p/kmansoft/wiki/FasterScrollerView

http://stackoverflow.com/questions/4485170/android-scrollbar-with-a-extra-view-screenshot-included

So Yes, these are not just useful on the desktop, but on a number of touch apps too.