In my case, I want to perform adds first, then modifications, then deletes. This is because updating my website involves adding and deleting .tar.bz2 files (which are large), and modifying .html files that link to the .tar.bz2 files. When adds, modifications, and deletes are unsequenced, this could cause broken links while the adds take about an hour to upload. I work around this by manually uploading the large files that I'm adding, then running synchronize.
Other users might want to sequence adds, modifications, and deletes in another order. For example, users who are close to running out of space may want to sequence deletes before modifications and adds.