So I see there are two customizable buttons on the underside of the P4 controller...

Who is going to do what with these?

The P3A/P3P have those buttons, too.

By default, one toggles between follow and FPV camera mode; the other drops the camera 90 degrees down/up.

They can be customised to fulfil other functions, but there aren't a huge number of options.

Since you can already tilt the camera down with the toggle, I switched mine show the the advanced camera settings so I can adjust them more quickly.  

You can set the two buttons as some commonly used functions such as the battery info page and video channel page. You can set it in the app.

What about to reset the home point?