Live regions are essential for content that updates without a page reload, such as form validation errors, a shopping cart item count, a chat message arriving, or a loading status message; without one, a screen reader user would have no way of knowing the update happened at all.
The aria-live attribute takes a value of “polite” (waits for the screen reader to finish its current announcement) or “assertive” (interrupts immediately, reserved for urgent, time-sensitive updates). Overusing assertive live regions is a common mistake that overwhelms screen reader users with interruptions.