What do you do if you want to experiment with lower prices? If you lower the price for existing customers during the experiment, it's going to hurt if you end up putting the price back.
Adjust the terms as needed.
Not sure if you mean this, but the problem I find with offering sales (where you mention the end date) is you can't tell if some customers are only buying it because they don't want to miss out on a limited offer so it doesn't help you learn the real value of your product.
Like when people buy clothes in a sale they end up never wearing, or people that buy Steam sale games and never play them.