Just a short list:
- the deaf
- the mute
- the very socially awkward
In the last category: I can personally attest that I've put off scheduling an appointment with someone I've done business with in the past for two days, purely because the thought of actually picking up the phone and going through the process of aligning our calendars makes the hair stand up on the back of my neck. If I can pass that task to an assistant, my life would be much easier.