Nope, it probably isn't best for performance. It wasn't my call to make, and it has been operating like that for years.
But for data stability, I see why it was done. It is a trade off, one that we may reconsider down the line.
Edit: Misread the question. I'm not exactly sure, but it significantly improves speed, enough for us to complete the migration, then switch it back on during production.
One note: when running on a VM, it seems not to flush to disk regardless of the OS setting. Probably because of the virtualization software
