Yr friend might talking about
At the time of RFE or local interview.
i.e. you should be in a job that is the same or similar to the one your LC is approved for
1. At the time of responding to an employment RFE generated by INS
2. At the time of an interview at local INS (Random 5-10% of applicants get this)
AND
3. for a reasonable period of time after GC approval...(reasonable is the operative term can be intreprested as 6mos, can be 2 years )
If you do not anticipate the first 2 to happen to you , you can moonlight or flip burgers while on EAD.