MP3 is lossy, so editing or re-saving it repeatedly degrades the sound. WavPack shrinks audio without losing any of it. MP3 is at home in music and podcasts that must play anywhere; WV is the usual choice for archiving CDs and recordings without losing anything. WV cannot bring back detail that MP3 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.
This pair uses the compatibility engine, ffmpeg built for the browser, because WV cannot be written by the browser's built-in codecs. It is a one-off download of about 10 MB that the browser keeps, it is slower than the built-in codecs, and it takes files up to 1 GB.