FLAC files are large, and Apple Music, many car stereos and older players will not play them. CAF is what Apple's audio tools and iOS apps use. FLAC is at home in archiving music at full quality; CAF is the usual choice for audio inside Apple's apps and development tools.
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 CAF 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.