Jeremy Fox has a recent post that discusses reasons for starting a science blog... or for not starting a science blog. The Dynamic Ecology blog is a group effort, but the group consists of academics. As a non-academic (industry) blogger, I had a different set of issues to contend with when starting to put my ideas out for public consumption.
Public outreach: I don't have any metrics or get any "points" for public outreach. I like public outreach, and I enjoy being out there in the field as a visible lady scientist, and I'm happy to answer any and all questions while I'm working (to the extent possible). But my job doesn't have any components at all related to educating the general population about scientific topics. It would occupy the same space on my résumé as volunteering for the local food bank - a nice do-gooder hobby that would only be useful in that it could be thought of as a form of networking. So, blogging wouldn't help my career that way.
Research publicity: One of the big differences between academia and industry is the focus of the science/research. In academia, I could work on my own thing and (at least in theory) be beholden only to Science. I work for a client, and my work product is owned by the firm. Depending on what I'm doing, my work may end up in the public domain in the form of public documents/filings. But the actual intellectual work - the arguing over cause/effect, the loose ends that need to be explained, the division of the workload, the polishing of the text? All that messy stuff is hashed out in private among a group of scientists prior to document finalization, whether that document is a memo to the file, a letter to a regulator/opposing counsel, or a big report. For me, there is no upside and a whole world of hurt if I publish internal deliberations for a recognizable product.
That's ok. I'm having fun over here even though my blogging will likely never have a positive career impact - it isn't intended to.