It provides a quick feedback loop when you're trying to poke at stuff on-screen with your fingers. Which is nice since it lets you know quite seamlessly (1) how good your aim is, which gets kind of critical when using fingers on a touchscreen compared to a mouse. and (2) whether a tap has even registered in the first place, which is often problematic for many users who may be wearing gloves, have drier skin that doesn't register as easily, etc. etc.