Why should one add ID to their HTML tags?

Question

A simple question: why should we add the id into our HTML tags if they work perfectly well without them? I know that one of their uses is being able to navigate

Answer 1

Uses of id attributes in HTML

• As a target for a fragment identifier on a URL.
• As a target on form controls for the for attribute on and
  elements.
• As a target on
  elements for the form attribute on form associated elements.
• As a target for element references via the microdata itemref attribute.
• As a target for element references via some ARIA attributes including aria-describedby, aria-labelledby and 4 others.
• As a target on elements for the headers attribute on and elements.
• As a target on elements for the contextmenu attribute.
• As a target on elements for the list attribute on elements.
• As part of a hash-name reference to elements for the usemap attribute on the and