What is the second screen function on PS4 second screen for?

So I just downloaded the ps4 second screen app, but there's a feature called second screen does jmd know what it is for?

You can use the picture that your ps4 gives e.g. Stream on your ipad etc. And then play on the ipad or pc. But that only works if you have a decent internet connection

All you have to do is download the corresponding app onto the device

With the app you can play along with the controller on your mobile phone. Wouldn't recommend it, however, as many cell phones either can't get enough of the line or it generally jerks again and again or there are delays.