Watch the Between The Thirds online guitar lesson by Jennifer Batten from Rock Sauce For Lead Guitar
Bending half steps, whole steps or larger intervals have a harmonic purpose. Unison bends are just a sound effect since you're hitting the same note in different ways. Unison bends are a Jeff Beck signature sound. You can for instance bend a D on the B string up to E, followed by playing the E note on the E string (12th position). But you can also play a unison bend with the index finger i.e. (in 12th position) play a G on the G string, bend it up to A and follow it with an A at the 14th fret. This one is a bit more difficult.