java Holder vs document-style, or why use Holders

I've started to use document-style web-services recently. I've learned that in this way we can have only one part("parameter") for input/output message, which can contain all data.
But now I've read about Holders, which, according to this link, is used to return multiple parameters. Now I wonder, why should I use Holders, if I can use the document-style response, which can contain everything?
Additional info I found here still left me uncertain.