Since you have placed this in the Business section, I will answer in that context. The purpose of word processing is to create documents that are needed for business purposes. These can be things like memos written to others in your firm or like reports to your bosses. The major benefit of word processing is that it is more efficient and therefore economical than other ways of creating written communications.
As an example of this, word processing now makes it very simple to create form letters that are sent to multiple people and which vary only in a few details. For example, imagine a form letter that tells each customer what they owe at the end of a monthly billing cycle. With word processing programs, the letter can be reproduced easily with each person’s name and account details automatically put in a separate letter. In times past, this would have required each letter to be typed separately. This is one reason why companies in the past would have “stenographic pools” of secretaries who would take dictation and type communications.
Word processing can be used to create written business communications much more easily and efficiently than was possible in the past.