Not everyone has their MIDI controller or keyboard in front of them when they compose or audition sounds. Their keyboard might be off to the side, or perhaps they are traveling and they just have their laptop available to compose with.
Having a way to audition sounds by playing them with a qwerty keyboard and controlling the pitch bend and CC1 information with a mouse/trackpad is useful in these situations.
For people like me, who own a digital piano that doesn't have a pitch bend wheel, I will actually use the pitch bend UI element in the sample player.
If anyone knows of a stand alone pitch bend wheel that I can pair with my digital piano, I'd be interested in that.