Inherently "sticky" elements in desktop and mobile UIs, Tooltips have been around for quite some time. You can argue that they are outdated, but there is still a place for them to be used in modern web and app UIs. Nowadays, Tooltips are mostly used to provide information about an element when hovering over it, or to direct and guide users where to take action next.
Using Tooltips with some degree of thoughtfulness can help create a great user experience (UX). Used over and over again for every button and link, Tooltips will quickly become tiresome. As always, knowing when to use Tooltips is just as important as knowing how to use them.
This blog describes the best practices of Tooltip.