What is the use of <aura:set attribute="else"> in Salesforce lightning component?

Hi,

aura:if evaluates the isTrue expression on the server and instantiates components in either its body or else attribute. Only one branch is created and rendered. Switching condition unrenders and destroys the current branch and generates the other

<aura:component>
    <aura:if isTrue="{!v.truthy}">
    True
    <aura:set attribute="else">
      False
    </aura:set>
  </aura:if> 
</aura:component>