+1 button will make your website crawled by google robots very quickly
Today I make more tests, now I get the conclusion: +1 button will make your website crawled by google robots very quickly. If you launched a new website, you should add +1 button in the website, then you signed in with your google account to click +1 button. Soon you will find your website get crawled by google robot.
In the past, google search ranking is emphasis on the external links of a website, now I thought +1 button become more and more important. If you have a strong google+ account(many people circled you), your google+ will be your good tool to make SEO.