Google has rolled out a small update that makes the tagline in your profile very prominent on their Google+ platform.
Google now shows the content you place in your tagline in the hovercard that appears for your profile.
Google+ Chief Architect Yonatan Zunger spoke about this update:
Oh hey, we launched a minor feature yesterday that makes me happy: if you fill in the “Tagline” field on your profile, it now shows up on your hovercard. So that’s a great place to put a few short words about yourself; it’s the first thing most people will see about you, after your name and pic. The hovercard, if you haven’t heard the word before, is the card that pops up when someone hovers over your name.