This is a rhythm guitar exercise pulled from one of my tunes, "Fatherland". As you can see, I'm tweaking my vibrato in between lines in this section on the rhythm guitars. Also note that I only have time to move note "E" in one direction before I to play again. I'll A and B it for you in the demonstration.
See how this has become a nervous tick for me? Instead of playing it bland a straight, you can tweak your rhythmic lines to your liking as well. It's a cool little discovery I found studying guitar players like John Petrucci and Mark Tremonti.
In the next three demonstrations I'll provide various situations where I use vibrato to embellish my lines.