On windows, you need cygwin or similar to run rsync.exe, which can complicate the deployment of your desktop app or shell extension.
I tried deploying updates to a (pre-existing already deployed) website to a Windows-server machine using rsync once.
The site which running fine in the first place instantly stopped working, because rsync didn't merely copy the files over, but it completely reset the existing ACLs and permissions on all the files. The result was that the webserver no longer had permission to access the website's files. It was repeatable for every sync.
I tried deploying updates to a (pre-existing already deployed) website to a Windows-server machine using rsync once.
The site which running fine in the first place instantly stopped working, because rsync didn't merely copy the files over, but it completely reset the existing ACLs and permissions on all the files. The result was that the webserver no longer had permission to access the website's files. It was repeatable for every sync.
Needless to say, I found it less than optimal.