Wearing a suit to an interview is not always appropriate. My current job is very tech-heavy, and I knew the work atmosphere was very casual. Wearing a suit might have actually alienated the people interviewing me. Instead, I wore business casual, plus a tie. After the interview, they suggested we all go to lunch, and I took the tie off.
By not coming across as a "professional interviewee", I connected with the engineers interviewing me, and they gave me a glowing recommendation. If I had come in wearing a 3-piece suit, they may have wondered if I was there for a salesperson job.
I've since helped interview others for our team, and I can tell you that dressing up doesn't help at all. You need to be able to discuss your tech skills, and come across as someone who will "fit in" with the team. Looking (and acting) like a prima donna will not help.
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