Zipping a file repeatedly typically doesn’t reduce the size further after the first time.
Not sure what the original point was but curiously I happened to use file
on a an Apple .numbers
file recently and found that it was a .zip
file in disguise with zero compression.
So maybe the point was that it’s used often as a container format more often than it’s used for compression? Just my (unrelated) general computer work would also suggest this.