What is the use of notifilib in salesforce lightning component?

Messages can be displayed in notices and toasts. Notices alert users to system-related issues and updates. Toasts enable you to provide feedback and serve as a confirmation mechanism after the user takes an action.

Include one <lightning:notificationsLibrary aura:id="notifLib"/> tag in the component that triggers the notifications, where aura:id is a unique local ID. Only one tag is needed for multiple notifications.

Notices
Notices interrupt the user's workflow and block everything else on the page. Notices must be acknowledged before a user regains control over the app again. As such, use notices sparingly. They are not suitable for confirming a user’s action, such as before deleting a record. To dismiss the notice, only the OK button is currently supported.

Notices inherit styling from prompts in the Lightning Design System.

To create and display a notice, pass in the notice attributes using component.find('notifLib').showNotice(), where notifLib matches the aura:id on the lightning:notificationsLibrary instance.

Here’s an example that contains a button. When clicked, the button displays a notice with the error variant.

<aura:component>
<lightning:notificationsLibrary aura:id="notifLib"/>
<lightning:button name="notice" label="Show Notice" onclick="{!c.handleShowNotice}"/>
</aura:component>