A raw AAC file has no container, so some players cannot seek in it or read its tags. WAV is uncompressed, so audio editors and transcription tools accept it without fuss. AAC is at home in efficient audio for streaming and video soundtracks; WAV is the usual choice for recording, editing and mastering. WAV cannot bring back detail that AAC compression already removed; it simply stores the result without further loss, in a larger file.
The defaults suit most files. Under Options you can trim the start and end.
The conversion uses your browser's own video and audio codecs (WebCodecs), with hardware acceleration where the device has it; the file is read from disk as it goes and can be up to 2 GB. Where the browser lacks a codec, the page falls back to the compatibility engine.