I do think negotiating a job offer is very important. It doesn't benefit anyone if you are feeling undervalued/underpaid at a job. Work performance will take a hit, team dynamic will slowly shift, you will wake up every morning dreading to go to work.
However, I do think there is a need to resist the urge to treat negotiation like a game. Sure you may have gotten the best offer possible for your skills/experience, but how much do you need to be satisfied and do your best work? If you get hired having massively oversold yourself and the value you bring to the team, are you sure that would be a good start for your new job?
I recently negotiated a 7.4% increase on my base pay for a new job. I could have easily negotiated a 16% increase but I didn't. I want both parties to start the relationship happy. If either side feels like "did I just get cheated out of X?", that is a loss for me. Sure, any relationship may go bad, but why start a relationship if it's not going to be sweet to begin with?