It's just easier for me to press the pad down with my thumb (which is already resting on the pad) than it is to pick my finger up, then tap the pad, then put my finger back on the pad to move the pointer somewhere else.
Also, dragging using tap to click is something I've never really understood.
Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 5_0_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A405 Safari/7534.48.3)
The photo actually can't be trusted because it's heavily photoshopped. Not only is it blurred, but when you hold your finger on an app for even a second, the app dims.