Blogs offer a more rich publishing platform and people subscribe to see their content. Many sponsors are accustomed to rating online influence by monthly traffic to a blog. So while some people have found success becoming "Internet famous" and are sponsored simply to post on social media, other corporate sponsors haven't broadened their criteria beyond more lasting content delivery platforms like +WordPress and +Blogger.
One of the ways they evaluate your content is using +Google Analytics to measure monthly visits to your blog. So even if you've been somewhat successful marketing though content, engagement and building a following on social media, you may find that the sponsors you'd like to connect with are using other metrics to evaluate potential marketing partners.
Posting to blogs adds yet another location to post to, and it is a good idea to have unique content there utilizing the added features such as the ability to include multiple images. But all of your work on social media doesn't have to go go waste. To some degree your audience varies from site to site on social media, and who is online looking at your posts varies, so allowing your social media posts to aggregate to a blog can give your friends and followers a single place to see your recent content. If you do a good job curating the site and attracting people to come back over time, your potential sponsor will like it as well.
I had a nice experience with the Google+ to Wordpress plugin for Wordpress this morning. The founder of photo sharing site +500px, +Evgeny Tchebotarev, tweeted to his 5000+ followers one of my Wordpress blog posts created from a Google+ post: https://twitter.com/
Image Buyers Are Using @500px Prime, says @JeffSullPhoto http://t.co/7f6JfAFHr8I experience decent results on Google+ when sharing individual photos, but for some reason the filtering algorithms on Google+ seem to demote my album shares somewhat, more heavily restrict shares of other posts, and severely restrict shares of external links. Worst of all, much of the interaction I see is from users far from my target customer base, so Google's current heavy and skewed filtering algorithm renders G+ practically worthless in my experience. But I have a lot of confidence in Google to eventually correct course and get on a productive path. So although my initial 4-5 posts per day for its first year dropped to 1 per day for the next year and again to more sporadic contributions this year as the site fails to deliver broad engagement, when it eventually does, I want to be there. I've set up Google+ pages to use when they become fully functional, such as when they can connect with and follow (circle) more than a few users per day before maxing out some limit.
— Evgeny Tchebotarev (@tchebotarev) November 17, 2014
In the meantime, any work you invest to maintain a placeholder stake in G+, or to make posts such as URL shares which are likely to be barely distributed on G+, doesn't have to go to waste, since those posts can have a second life on your blog.
It's no small benefit that those blog posts aren't restricted by any severe filtering to hide them from your followers, as they might have been on the original social media site. One good tweet of your blog post, and it may have more potential viewers than the original post had on the social media site. And your social media sites may supply that traffic. Even if there are few eyeballs on your G+ posts or they're not views from your target customers or subscribed (circling) G+ users, there's no reason why you can link to the resulting blog post and drive traffic there from Facebook, Twitter, and so on.
If you'd like to consider having your social media posts mirrored to a Wordpress blog, take a look at the Google+ to Wordpress plugin: http://sm2wp.com/ You'll also see the Twitter version there, Social Media 2 WordPress for Twitter.
|Your G+ posts can appear on your blog|
Perhaps +Google will consider reporting our G+ activity in +Google Analytics so sponsors can see and recognize that as part of the value we offer. But the filtering of the distribution of your G+ posts may still impede their visibility on G+, so having them available on an external blog enables you to make full use of the content, while you have full tracking and credit for how many people view it (at least directly on the blog). It's surprising that Google didn't offer similar G+ to +Blogger post migration ages ago (and it's surprising that the existing Blogger to G+ posting capability suffers the same heavy filtering and reduced views that any other external link seems to experience). Google Analytics could offer the unique strategic advantage of reporting of the combined views of the same post on G+ and Blogger, but a great baby step in the right direction would be any reporting of G+ posts at all.