Why is the default umask 644 for files generated by www-data?

Question

System administration

Interested in a very fine line, why is 644 safer than 664?
After all, the file was already created www-data with the www-data group, what is the point of such protection?

Answer 1

The www-data group can include other users. Read it like "only the owner can change"

Answer 2

> umask - 644
or
rights - 644?
umask 644 is the right --xw--w-(122), what an exotic, the owner can run, and the group and others can write.