Rel="alternate" Tag Significance..? Help

Hi guys,


I have seen on so many sites tht they are putting something like

<link rel="alternate" title="" type="application/rss+xml" />

To give search engines an alternate XML page. So I want to clear how much it is benifitial for a site to put a link like this.

and can i put this links on every web page providing its alternate page.

One is SEs dnt have to crawl the page it ll directly get links & text (content) from page.....need to know other benifits & risks....

You can specify alternate pages that are specifically optimzied for rss-feeds aplications or for users using a mobile:

ex:
<link rel="alternate" media="handheld" href="alternate_page.htm" />