Doesn't feel like much of an explanation to me.
# UMASK is the default umask value for pam_umask and is used by
# useradd and newusers to set the mode of the new home directories.
# 022 is the "historical" value in Debian for UMASK
# 027, or even 077, could be considered better for privacy
# There is no One True Answer here : each sysadmin must make up his/her
# mind.