Sometimes it seems like the practical benefits are hard to quantify.

Search engines already pick up and parse microformats (see e.g. https://support.google.com/webmasters/answer/99170). I believe hCard and hCalendar are fairly well supported--and if not, plenty of sites are using it, including places like MySpace.

It s the idea that adding CSS classes and specified IDs make your existing content easier to parse in a machine-readable manner.

hReview is starting to make some inroads, and hResume looks like it take off too.

I heavily use rel="nofollow" on uncontrolled links (3rd party sources) which is actually a microformat.

Check the microformats wiki for a decent starting point.

It just means your viewers can share a few generic "formats". You can generalize stylesheets, and parsing mechanisms. Rather than having a webpage consist of one "html document," you have a webpage that consist of "10 formatted micro-documents".

If you need a real world analog: think of it like attaching a formatted invoice, to a receipt, and a business card, rather than writing it all down on notebook paper with your left hand.

Overall the site becomes easier to digest for the rest of the internet. The data can be reused, combined, cross-referenced, and saved.

A simple example would be to have anywhere on the site a latitude and a longitude (geo). With Microformats, anybody that searches for that latitude and longitude can be easily referenced to their website, increasing traffic, awareness of that person / company, and allow users to easily save that information. (Although I ve encountered little of this personally, this is more of the future of things than it is current. But always good to stay up to date).

A second example would be a business card (hCard) where a browser can easily save and transfer it to an address book, so that just one visit to the site and the visitor has the information saved locally. Especially useful if they re getting hits from a cell phone.

I wouldn t recommend using microformats for "every possible thing". Use them for things where you get some benefit, in exchange for the effort of using them.

The main practical benefit I m aware of is customised search engine results:

• https://support.google.com/webmasters/answer/99170

Technically, Google now prefers this to be implemented using microdata (i.e. itemprop attributes) rather than microformats, but it s the same idea.

Having a micro-format can be better than no format since it lets you save every possible thing in the application.

A micro-format for every possible thing can be better than a standard format only because: it s quicker to create so it costs less and it take less space than some standard formats, like XML.

But all this depends on the context of the application and so you must explain it to the client in that context.

microformatting your content extends its reach in every, which way possible. using your sites structure as its "api" the possibilities are what you set your limits too