Simple formula:

It works for Google for the following three reasons:

1. Makes the users happier, and users get to see more relevant ads.
2. Makes the advertiser happier, showing more relevant ads, more likely to get results from the viewers.
3. Makes Google happier because with more users happier and more advertisers happier they make more $$$!

According to a recent SERPs analysis conducted by Search Engine Roundtable, Google is planning on enabling longer snippets that will allow Web sites to show up to 4 lines of text from the Meta Descriptions tag. This is important because it will offer Web sites the opportunity to attract visitors based on nicely and thought written value propositions describing the content of their Web pages. Hopefully the big G will also work around a way to prevent people from stuffing their new “spacious” meta headers with useless information!