WAV stores sound uncompressed, so a minute of CD-quality stereo takes about 10 MB. That's awkward to send or keep on a phone. At 192–320 kbps an MP3 sounds the same to most listeners and is several times smaller.
Add WAV files above, pick a bitrate and download MP3s. For voice recordings and podcasts 96–128 kbps is enough, and the Mono switch halves the size again.