Your point that other filesystems get by without checksums stands, but Apple does not use ECC for all hardware. Also, we are left to wonder if their "reliable"

Your point that other filesystems get by without checksums stands, but Apple does not use ECC for all hardware. Also, we are left to wonder if their "reliable" SSDs are as reliable as checksums at the filesystem layer (or as reliable as both). I suspect the answer is yes, for the majority of applications running atop APFS (which is to say, iOS). Probably not for video assets on that Promise MPX bay (i.e. "external" non-Apple storage media).