While Google+ may seem dead to most of us, it's still a VERY useful term for SEO! Why?
Here are my top reasons:
When you post links to Google+, your pages get indexed immediately. So it's basically like telling Google personally, "Hey, I just put up a new page, can you index this new page for me now?"
Uploading images, links, information and tips to Google+ will just plant more seeds into the Google world for people to find.
You can also build themed Google+ Collections so you can post to different collections that could be found by other Google+ users if looking for specific topics. Below is an example of a Google+ page that I help post to for one of my clients, Sandiaseed.com. I post links to blog posts that we write that discuss relevant topics for her seed customers, like: "How to grow Hatch chile" or "Weak Pepper Seedlings." Once we add new blog posts, content, or products to her website, we post on Google+ to immediately get Google to see this great new content.
So make sure not to overlook Google+ as an important tool for promoting your website. Everytime you add new pages, blog posts or other information to your website, let Google know to check it out right away by simply posting to your business Google+ page.