The added pressure of the audience is quite significant. It's like the difference between singing in the shower and singing on America's got talent. Being in front of the public makes some people very uncomfortable. Performing in front of an audience can also be very intimidating. The audience brings out all these factors that one must deal with within their own head as well as worrying about the opponent who's intent and preparation is to put you down.
Competing in front of a crowd can be interesting. I'd rather compete in front of a hostile crowd than one rooting for me. I never want to let down a friendly crowd.
I remember the first kick boxing match I was in. It was in front of a friendly crowd. I was nervous about letting them down. One of my corner men was a fellow black belt and best friend. After the first round, sitting on the stool in the corner he said to me, "Can you believe they're paying you five hundred bucks for this? You're buying dinner later, chump". And all my nervousness went away.
Years later one of my black belts had a PKA match. We were in his opponents home town. A bunch of us were sitting in the stands before the fights as the crowd was filling the stands. He comes out to inspect the ring. He's walking around and looks up to us and yells, "Hey! Do you want me to drop him here [he points to a spot on the apron] or here [points to a another spot.] Boy, did people start to boo him. And I'm thinking, "What the hell is he doing, that's not like him".
But he yells it again until one of us answers, we picked the first one. Then the booing really started.
Second round he dropped the guy with a right hand, left hook combo. EXACTLY in the spot we picked. That crowd went so silent you'ld think somebody pressed the big Mute Button of life.
Later he told me that he was informed that his opponent did not do well with really confident people, that's why he did it. AND that the spot the guy landed on - was pure luck.