If you work in sales ...

Personality type can help you to understand

• which clients will want lots of information, and which ones will be annoyed by that, just wanting the bottom line
• which clients are best pushed for a quick decisions, and which ones would leave and never come back if you did that
• which clients are open to and like new ideas, products, etc, and what to do to help those who aren't to take a second look
• which clients need you to make some small talk first, and which ones hate that

It is about understanding people's preferences and communicating with them in the way that they like best.