An option to skip, overwrite, or rename duplicate files.
For example, the program should recognize that when I am redownloading a channel, it should ask to skip the videos that already exists in the download directory, so I can easily update my library without figuring out which videos I'm missing or having to go through and delete any video with a (2) from the queue.
A duplicate remover would be great as you could download lists and playlists and not have to worry about duplicates or having to spend hours removing duplicates.