SSDs use CRC to deliver their probabilistic data storage approximation. FS level checksums are, among others, for when that fails.
FS level checksums also cover bitflips on your bus during the write phase (the drive will crc the already bad data) or during the read phase (you receive different data than your drive sent).
FS level checksums also cover bitflips on your bus during the write phase (the drive will crc the already bad data) or during the read phase (you receive different data than your drive sent).