When the -R option is specified to reject files by name in recursive mode, wget downloads them anyway then deletes them after downloading. This is a problem when you are trying to be picky about the files you are downloading to save bandwidth. Since wget appears to know the name of the file it is downloading before it is downloaded (even if the specified URL is redirected to a different filename), then it should not bother downloading the file at all if it is going to delete it immediately after downloading it.
- Jason Cipriani