Well, they can actually be helpful. I've found a lot of good info on company blogs from engineers about embedded programming, electronics, and other topics.
You can also think of it as marketing for engineer types who are usually immune to formal forms of marketing. Managers don't care about details, they want to see $ numbers. Engineer types want gory details. So your engineering blog can help market your products to engineers. Just look at intels documentation pages vs their actual intel.com site. intel.com is marketing 101 eyesore.
An example would be a blog from a semiconductor company making analog circuits. Think Bob Pease types. They'll talk about a specific problem or circuit, go into the bloody details, math, schematics, charts, graphs, etc. Then toss you a product from their portfolio that can solve the problem.
