It's less legislation on the floor at the same time so legislators can concentrate more on bills. They need to scrutinize and analyze and think. Otherwise you pass things with bad consequences like removing the right to vote of some citizens or don't catch typing mistakes. It's difficult to do good work when you juggle twelve bills at the same time. And the public won't even know what is debated or adopted.
Right, but even with 20 slots full all the time we still have a backlog of 14 bills after more than a month and despite already passing close to 30 this session. If we halve the bill slots every senate would be voting on bills introduced in the prior session.