MP4 is the world's default video: the file that plays before anyone has to think about it. It was born in 2001, the MPEG standards group, built on Apple's QuickTime design, and its real weak spot is very little day to day: as a container its quality depends on the codec inside.
WAV is audio with nothing taken away: every sample intact, every megabyte accounted for. Raw PCM samples in a RIFF wrapper. No compression of any kind. That makes it the right destination when what you need is recording, editing and mastering, where every last bit matters.