Why do Academics use Social Media and Blog?
Most likely not for public outreach seems the case. One recent article from The Guardian's section on Higher Education Network identified that the majority of academic blogs they investigated were focused on blogging for professional peers. While the 'study' had certain limitations (e.g. design, N, review process), I cannot say I fault them. I haven't come across many blogs that seem meant for those outside of academia or the authors field. And honestly I am no different, I hardly expect anyone that comes across my site and reading this stuff to not be an academic in the medical or pharmacy field.
But thats probably the point, whats the point? Many say academics should blog and micro-blog for outreach. Tell everyone about what we are doing and why it matters. But thats what the research is for, and maybe some academics don't want to share their ideas or projects too loosely, lest they lose any integrity or get scooped. Just as I have said before, I really have not seen social media as a way to increase 'collaboration' which is overall sad.
I do not think the vast majority of academics are ignorant of social media or blogging. Even 'how to' guides seem rather insulting at the best of times. The valuable ones I think are those that show how to set up a blog, technical aspects, and costs are valuable, and the experience being share is valuable. But saying what to write and such, I mean, aren't these people already for their ability to write? After all, they write papers that are published, give talks, and submit grants. I don't think topics is what they want. That is something that I wished someone had shown me, instead of having to self-teach myself all of this.
What Benefit does Blogging or Social Media offer Academics then?
Getting involved can be beneficial for multiple reasons, which I think @FutureDocs hit well her article "Twitter to Tenure: 7 ways Social Media Advances my Career." Outcomes can include further presence in your specialty or academic interest, allowing for interviews, grant opportunities, and potential dissemination of information. For me, I have met alot of people with similar interests on Twitter that has come close to turning collaborative. When I get a clear cut example I will gladly share it.
Limits of Social Media and Blogging by Academics
Personally, I will never write on the department meetings or back table talks that take place at meetings or other organization conferences here. It just isn't the place. And I think that is the fear, is that someone will say something they shouldn't, especially if they are writing under an anonymous name. I have no idea where social media and blogging fall under academic freedom for those on a tenure track, but that may be worth finding out for those looking to start. Lastly, determination of your institutions stance wouldn't hurt as well.