Good to know that your friend had no problems. Hope everyone who are in similar boat or will be in similar boat in future will not have problems.
It was just a thumb rule based on probably someone's bad experience, the individual involved has to make a decision about it based on the various inputs. If the specific individual involved things his case is clean and will not have problems of any kind, then (s)he should go ahead and follow his/er gut feeling. If (s)he is not very comfortable for whatever reason or problems faced earlier then do as you think is right after considering all the information.
I guess the general rule was put forth by lot of folks more out of the feeling that it is safer to stay and go than go immediately, but it is not a hard-and-fast rule and obviously is not a guarantee either. Anybody could get into issues with USCIS given the ways they operate. We can only make things in our control to be clean like birth certificate, marriage certificate, no DUIs, no arrests of any kind and trust the process and make all our documentations and processes we go through are very clean.
My $0.02.