Speed Suits reduce drag and help you go waaaaay faster. The more drag you reduce, the more faster you can go! If you don't wear one, you will have more drag, and you will go slower. There have been myths about the human thinking that you can go faster. Trust me, Speed suits will go faster. Take it from a fellow swimmer.
Although the they might not always help greatly...Speed suits do help swimmers go faster. They help because they reduce drag and help swimmers have a mind set that they are going to go faster which will make them go faster! Therefore, speed suits ARE needed in swimming events because they do help!