The New and updated file(s) only checkbox makes WinSCP ignore files in source directory for which there exist file in the target directory with the same filename and the same or newer timestamp. The option is available for SFTP protocol only.
Assume i transferred files from remote to local with option "preserve timestamp" set.
Assume i was forced to reset my comp or connection in the middle of that process.
So when i start comp again, i dont want to manually check which files, directories were transferred partly and which not at all. So it is reasonable for me as an user to assume, that i can give copy command to the remote "topmost level" directory i want to transfer and the program would resolve the differences for me (when needed w prompt dialogs).
Either the problem is in your help file(which is confusing) or in the missing feature of your program (which is essential functionality for coping large data with unreiliable internet connection ).
What does the "new and updated files" mean?
You dont say about the file size anything.
If it only means what it says, you definately need to enhance the functionality of program with the extra option about file sizes.
I mean if i before computer crash transferrerd some of my files partly from remote to local, they should have now in my case the timestamp of that of remote files.
So they are equal.
And by the definition of your help file shouldnt be touched/completed although only the file exists on local disk partly compared to remote file.
Thus timestamps equal but file content is not.
Which is bad.
This should be cleared up in help file.