How come Google+ could be useful for SEO or like facebok is used to grab traffic?

It hasn't found out but there are a lot of testing currently held on how Google+ affect one's site performance.

How come Google+ could be useful for SEO or like facebok is used to grab traffic?

First you should be aware that are you asking for SMM or SEO usefulness with Google+. As both terms are different.

well "prcys" i a asking about both. because SMM is also a part of SEO and while doing SMM of some site you are doing SEO too.

Google+ is social networking site and i think it helps to bring traffic.

Yes, it's going to do something similar to facebook likes.

Google +1 also has the ability to social network, so you could locate others with an interest in your interests if you wanted to also, as they could with you, which is where the real traffic potential would be in my eyes...

i had used face book and got huge traffic on my website but i haven't tried google+ yet, i hope it would be helpful.