Sending a thank you note or email after being interviewed is a must. If you don’t send one, you aren’t displaying common courtesy and may give the impression you don’t value the interviewer’s time, the job opportunity or your reputation.
This, of course, could directly (and negatively) impact the hiring decision. I know many managers who have not hired someone based on not receiving a thank you note, and as a fellow hiring manager, I have followed the same rule of thumb. In and of itself, sending a thank you note isn’t good enough.
If your follow-up note or email doesn’t generate excitement and keep you at the forefront of the hiring manager’s mind, all it does is help ensure you aren’t guilty of an interview etiquette blunder.