One difference between Explorer and File Manager is that with File Manager
you could open up two windows to more easily copy files between drives.
To do the same thing with Explorer:

Close all running applications
Start two copies of Explorer
Press Ctrl-Esc to bring up the task bar
Right click on an open space
Select Tile Horizontally or Vertically depending on your preference
Your two Explorer sessions will now split the screen and you can copy between them by
dragging files like before.