why is the output of `du` often so different from `du -b`

Question

why is the output of du often so different from du -b? -b is shorthand for --apparent-size --block-size=1. only using

Answer 1

Because by default du gives disk usage, which is the same or larger than the file size. As said under --apparent-size

print apparent sizes, rather than disk usage; although the apparent size is usually smaller, it may be
larger due to holes in (`sparse') files, internal fragmentation, indirect blocks, and the like