Addition to Performance/2.: Synchronization costs are typically the biggest deal in applications that involve I/O (e.g. hard drive or network). Try an average database transaction with and without synchronization. 1) On sqlite3, it's dozens vs hundreds of milliseconds. Bigger databases, probably not much difference. 2) Lookup NFS sync issues. It's a huge speed/safety tradeoff. 3) On some file systems, a debian installation may take 10 minutes or 90 minutes depending on whether you disabled sync (eatmydata command).