WAV files are about ten times larger than an MP3 of the same recording. FLAC keeps full quality at about half the size of WAV. WAV is at home in recording, editing and mastering; FLAC is the usual choice for archiving music at full quality.
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.