An interesting feature on some UAV's and perhaps something DJI ,may want to look at for the Inspire, is rolling record.

Basically, the Camera records everything on a rolling basis, like a surveillance camera, and if something interesting happens, you can hit record, and it will save the preceding 2 minutes and till you stop the recording

Makes sense, a lot happens with the recording button off :-)

can't you just start recording straight away or am i missing the idea

Post trigger could come in handy in some shooting scenario but it would be just as simple to record the entire flight. Also 2 minutes of footage (especially 4K) would take a long time to rewrite to the card -- technically not feasible on a small camera like the one on Inspire.