Imagine if all your business contracts were sent to customers written on postcards. Everyone who happened to see the postcard could see exactly what you were going to charge the customer, how many of your product the customer is going to order – and all of the information about the customer .
Your competition, naturally, could take that information and send a contract to that customer of yours that undercuts your proposal and offers better terms. They could also share that information with others to let them know that this customer buys from you. (Or, at least, they used to!) Your customer, too, could potentially see what you are charging other customers.
Now… STOP imagining – THIS IS HOW THE INTERNET WORKS TODAY!