Our scenario is, the remote files should be downloaded into folderA. And then they will be processed and sent to FolderB. But in some exception cases all files may not be downloaded into folderA. That's why to confirm all files were downloaded into folderA without fail, we need to verify all files at remote location were downloaded into folderB ultimately.
That's why, we need to verify all remote files against files in folderB and then download only missing files into folderA"
P.S - Another user on this forum with the name 'zenpie9' posted exactly the same question somewhere else, I will just post his question here with due Credit and Thanks to him.