I recently helped a friend setup for an event. It was a simple setup with 2 projection screens and a sound setup. He has seen me do it a hundred times and thought he could do the same by renting equipment and saving some money. It sounded good in theory but as the title reads production is not as easy as people think. In most cases there are always challenges to every setup, even events you have prepared for. There may be issues with not enough electrical outlets to carry the load needed. The batteries may die in the wireless mic, or there may be too much ambient feedback coming thru the speakers due to the way the hall is designed. There are a million things that could go wrong. Djs and anyone involved with production get paid for there expertise in knowing how to deal with these issues that WILL come up as my friend found out.
It was a good thing I was there to manage all of the issues. It saved him the embarressment in front of his friends and family. The sad fact is that if you are doing a good job nobody will notice, but if you are doing a bad job everyone notices.