Friday night weigh-ins started about 20 years ago with a limited number of clubs using them. The purpose of Friday weigh-ins was the same as it is now, it allows some of the mistakes in entries or bracketing to be caught earlier and be corrected. Plus, the host clubs typically have people working Friday night setting up, and it lessoned the wait for those weighing in Saturday morning. With the invention of split tournaments the benefit of a Friday weigh-in is probably less.