In the fight for the short attention span of our users, every performance gain, whether real or perceived, matters. This is especially true on mobile, where despite our best efforts at performance, a spotty signal can leave users waiting an interminable few seconds (or more) for content to load.

Design’s conventional answer to unpredictable wait times has long been the loading spinner; a looping animation that tells the user to “Hold on. Something’s coming,” whether that something is one or ten seconds away.

More recently, a design pattern known as progressive loading has gained popularity. With progressive loading, individual elements become visible on the page as soon as they’ve loaded, rather than displaying all at once. See the following example from Facebook: