Last month google decided to Change its index method and prioritize the Mobile version of any content.
Why it is?
While announcing this, google mentioned that most of search are coming from mobile phone and tablet devices but the search results and websites are ranked according to the desktop version. So they announced they will make a new change for indexing the websites based on mobile supported content? They Named this change as "Mobile-first Index".
Why its important?
Earlier 2012, google feels a massive increase google search from mobile phone. More then half perfect of all google traffic is coming from mobile phones. No its necessary for every webmaster to keep the website mobile friendly.
Hope this helps.