[Question] Why is writePrepared faster than writeCommitted?

[cwang9208]

The writePrepared policy writes the batch to the memtable in prepare phase, while the writeCommitted policy writes the batch to the memtable in commit phase. It seems the total amount of work to do during the entire transaction is not reduced. The writePrepared only moves the work of writing memtable to an earlier phase. So I'm wondering why is writePrepared faster than writeCommitted? The writePrepared wiki shows that writePrepared outperforms writeCommitted in the benchmark test.