Not just a funcitonal requirement, an emotional requirement
I’ve got a great new Nokia N80 phone. The front slides up to reveal the keypad. But it is an unsatisfying click. Functional, but not compelling. Compare this with the Samsung phones that slide with a Zhhhhhclunk. Both have the same function, but the Samsung feels better….
A few years ago I came across the term “psycho-acoustic engineer”. These are the people who work at IBM, Audi, etc. designing the satisfying “clunk” on luxury car doors. Apparently you could make the door close completely silently, but they decided that would worry people.