This is a good SEO practice for both robots and humans. Let’s face it. We humans are too busy to read to the end of a long title to find the term we’re searching for (I know, it’s pathetic).
Again, you can see an example of this tactic in this post’s title with the keyword phrase “content strategy” placed at the front of the headline. Colons are your friend for this method, but make sure the keyword is relevant. In this case, we’re going from a general topic to a specific topic that lies underneath that “umbrella.” But the dual purpose of something like, “Unicorns for Sale: 12 Reasons Why We Love Unicorns” can turn readers away — the second part may catch the eye of fantasy genre fans, but they would likely avoid clicking on the post because the first part (“Unicorns for Sale”) looks like a spam email header.