Windows has a general way of selecting the operation performed by drag&drop.
To copy, hold down
Ctrl key while dragging. To move, hold down
Shift key. And to create a link/shortcut (not applicable to WinSCP), hold down both
What if you want to make “copy” the default operation? Older versions of WinSCP could not do this. It is always the target application (Windows Explorer usually), that selects the default drag&drop operation. The only thing that WinSCP did, was disabling move operations all together using Allow moving from remote directory to other applications preference option. This forced Windows Explorer to use “copy”, because there wouldn’t be another option. Note that WinSCP actually disabled “move” by default, so you have probably enabled it yourself, if you face the problem.
The latest beta version does not have this limitation and always defaults to “copy”, even when it allows “move” too.
There is one trick to allow both move and copy while making copy the default, even with the old versions of WinSCP. Windows Explorer select its default operation using a simple algorithm. If you drag files within a drive, it moves them. If you drag files between two drives, it copies them. When you drag files from WinSCP, Windows Explorer thinks that they are in the temporary folder (read more about this). So if you have more then one drive in your machine, and there is a particular drive that you usually drag files to, then place your temporary directory on any other drive will give you copying by default. You can change the location of the temporary directory in preferences.