This undeservedly forgotten feature allows the user to start a gesture from any edge of touchpad, and then move finger in circle way across all the touchpad to scroll the document – something similar to the classic iPod's scroll.
Here's really old but gold video illustrating the feature:
This method has one huge advantage over repeatedly requested side edge scroll, which is – scroll is not limited by the physical size of the trackpad, which means the user could scroll continuously using only one finger.
In modern systems, from what I've found, this feature is only implemented in KDE Plasma (Linux), and in this small utility for Windows 10.