Let me re-phrase the question this way:
Does a normal person need an account on each of the social platforms: Google+, Facebook, Twitter, LinkedIn, Flickr, Instagram, Pinterest, …?!
From blogging prospective, I need the following:
Announcements & updates
I might need to send a status update every now and then. Twitter does it perfectly. Honestly, Twitter is my preferred one. I use it to express my tech opinions too. But whenever a tweet isn’t enough, a blog post can do it. I might also tweet links to some of my blog posts.
G+1s for the links of my blog posts
Yet it’s a perfect tool that has the best of all other social platforms, Google+ couldn’t compete with Facebook and Twitter. I still need the +1s though. I’ve talked earlier about the importance of Google +1s for the blog posts. So, I’m having the links of all my blog posts being shared to my Google+ account in a hope they get more +1s.
FB Likes for the links of my blog posts
To avoid bothering friends and family with my business issues or hobbies, I created my Twitter account. I also had to create a Facebook page for the same purpose and to be a place where I share the links of all my blog posts hoping they get as much FB likes as possible. As I mentioned earlier in another post, the number of Facebook Likes might not be as important as the number of Google +1s.
I store my pictures on Flickr and use them directly from there on my blog to avoid storage limitation if any. I used OneDrive once – check my other post (HERE). I also considered Instagram before getting back to Flickr. However, I found Flickr is more organized. Instagram is photos social tool rather than a storage tool. As for videos, I use Dailymotion.
Unless you’re a very famous person that has a lot of (real) followers, social media are not good in this part without paying money. This point is very arguable though. Personally, I use Twitter ads as I explained in “How to drive traffic to your website” article…