I've been looking for a way to easily compress my .js locally before deployment. I finally found a command line batch script that works with YUICompressor and Packer.
The problem I was having was that Packer was corrupting my files. Figuring it was an older version, I just manually took my YUIcompressed .js and ran it through the online Packer.
The result is that PACKER only reduces my YUIcompressed ..js by about 1%. Hardly worth the effort, it seems.
That said, I don't know much about Packer. Doing some research, it seems that YUICompressor and Packer are really both separate .js compressors. Is there really a need to use both? Do people use both? If so, why? Does Packer do something above and beyond compression?