Nothing much.
I attended the interview three times all in different styles.
- The first one was with a moustache.
- The second one where I was clean shaven.
- The third one was with a French beard.
All three times I got almost the same marks. I got selected in both the second and third time. It had more to do with the questions they asked and the answers I gave and some amount of luck.
Don’t ponder over trivial things like these. If you think the beard doesn’t suit the occasion, you shouldn’t sport it. Else, jolly well keep it.
There is no written rule that says sporting a beard is informal. For proof, look at our foreign secretary or our Prime Minister. Former is part of permanent bureaucracy while latter is from the temporary bureaucracy.