Content recommended by friends or acquaintances is often more relevant than content recommended by strangers. This is the core belief behind the +1 function.
But thanks to Search plus Your World, the +1 can also affect users who aren’t signed in to Google+, because instead of seeing which of their connections have +1’d the content, they can be presented with the number of people in their geographical area who’ve done so. This also suggests a degree of relevance to the link.
It is suggested that a +1’d link is likely to have a higher Click Through Rate (CTR) and in turn is likely to be shared more through social media such as Facebook, Twitter and Google+
A +1 from Google can lead indirectly to a higher page rank. The greater number of +1’s increases a link’s potential for a high CTR, which could lead to increased social sharing, and in turn can increase its Google search rank.
Importantly, because the effects of a Google +1 are indirect, your company should not ignore traditional SEO methods because established SEO work, from link building, keyword inclusion, URL structure and more continue to have a greater impact on page ranking than the Google +1 effect, the Facebook ‘Like’ and the re-tweet.
The Google +1 feature is still in its infancy and a greater study of its effects can be observed over time. In the words of the search engine powerhouse: "For +1's, as with any new ranking signal, we are starting carefully and learning how those signals affect search quality."