This is special Desktop hack used in latest versions of improved TOS - iTOS 1.04 and 1.62 .
Especially useful in case of many hard disk partitions.
Instead having lot of drive icons on Desktop it is possible to change drive icon's letter with simple holding down of new (desired) drive letter and clicking on icon.
In YT video is visible that count of drive icons on Desktop is limited. And in low res it is less, because drive icon takes 1/16 of space. And there are icons for floppies, trash can. Not to mention time needed to create them.
So, I think that 2-5 drive icons are enough, and when need to access different partition (logical drive) can just change on of them to it.