Three hours and four banana margaritas later, you return to find the copy operation choked on the tenth file because the file was open on another screen, or had an error, or was read-only. All your computer has been doing while you were gone is display a message asking you what to do about it. This is when we know computers are not like people.
Even the dumbest human would put aside copying that one file until you returned. So will Ycopy. When Ycopy finds a file it can't handle, it makes a note about it, and moves on to the next file. When you get back from lunch, you still have to do something with the recalcitrant files manually, but at least all the other files are taken care of.