set group id on directories

[marc () tky icdc fr (Marc Samama)]

I'd like to know if a sgid bit on a directory represents a security risk,
given the fact that the directory is not world or group writable.

On my system, whereas the manual states that this bit is ignored on 
directories, a file created on such a directory is owned by the same 
group that posses the dir, and any child directory has the same sgid bit,
by default.

It this feature commonly used anyway?

Marc.