Set GID's

how can one missuse a Set GID on a directory like
/etc, /usr, /sbin, /var, devices...????

i have found the answer to my own ?. so here it is:

if you have the SetGID set on a directory you will grant group permissions from that directory to any new file or new dir that is created under that dir...
so if you have Set GID set of /etc and you create a file under /etc after the SetGID is set that file gets the /etc directory's group id...(which is SYS)

Thanks for following up. I didnt know the answer to this one. Interesting...