user management – SETGID_HOME = yes had some side effects

In the documentation (comments) of the configure directive SETGID_HOME (/etc/adduser.conf), it is said that:

# If SETGID_HOME is "yes" for users' home directories with their own group, the setgid bit will be set. This was the default for << 3.13 adduser versions. Because it has negative side effects, we no longer do it by default. If you wish, you can nevertheless define it here.

What are these side effects?