I get it...it's hard enough to make time to blog as it is, now I am asking you to jump through one more hoop.
The truth is, that if you aren't tagging your images every time, you aren't reaping all of the benefits of having interweb real estate. Not only does optimizing your image filenames and alt text make it easier for Google Image Search to better understand your image, but it also gives people yet another way to land on your brand's webpage.
There is nothing worse than "pinning" an item from someone's website and getting a bunch of gibberish as the file name.
If you want the long answer, feel free to email me at email@example.com. I'd be happy to explain all of this in further detail.