Nonverbal communication is often used because

it is precise

it is easy

it is necessary

it is appreciated

It is appreciated

Explanation:

-Nonverbal communication isn't precise at least 65% of the time (Not in terms of sign language)

-Nonverbal communication is not easy at all it can be actually quite difficult to understand (Unless you have an establishment of basic movements to replace certain terms. For example, one finger up means "I need a new pencil" [Referring to a school setting])

-Nonverbal communication is most certainly not necessary, especially if you have the authorization and the capability to talk

-Nonverbal communication most definitely can be appreciated in certain environments (i. e. School, library, etc.)