Contrast is vital for persuasive communication.
One of the rules in writing sales copy is that if everything is a great deal, then, in fact, nothing is a great deal. The seller sets the benchmark and the buyer is persuaded, or not, based on the contrast that is offered. Therefore, contrast is vital for persuasive communication.
When we communicate, providing the brain with two options for response or action, our customers are more likely to choose one of the responses. This is something advertisers know and use extensively when building marketing campaigns.