Two plugins both think they own the price, and the checkout shows a third number
A dynamic-pricing plugin, a customer-group discount plugin and a coupon system get installed at different times by different people, each solving a real problem at the time. Run together, they apply in an order nobody designed, and a customer's final total occasionally does not match what any single plugin's settings would predict — a support ticket that takes an afternoon to trace and a discount taken directly out of your margin.
What you see instead
One clear pricing hierarchy, documented and built as one piece of logic rather than three plugins arguing, so the number at checkout is always explainable and always the one you intended.