Currently, if a legislator happened to have a sneaky agenda up their sleeve to write in a rider to a popular bill, they could do so up to the very last minute before a legislative vote. I don’t know how often this happens, but if it did, Prop 54 would help control that.
Prop 54 seems to borrow from the Brown Act, requiring any bills which go before a vote to be posted for at least 72 hours online. Also, the legislature would have to ensure all of its public meetings were recorded and the videos posted online within 24 hours.
This one seems pretty obvious. A YES vote would enact these changes. A NO vote would keep things as they are.
Here’s the state’s Legislative Analyst’s Office’s take: www.lao.ca.gov/BallotAnalysis/Proposition?number=54&year=2016