If you specify I/O priority management, workload management dynamically sets I/O priorities based on goals and I/O activity, and includes the I/O information when calculating execution velocity. So you might see some changes in your velocity values. The recommended setting for I/O priority management is YES.
The new DASD I/O using and DASD I/O delay samples are reported even when I/O priority management is turned off. This allows you to calculate the new velocity values to plan for velocity changes.