What exactly is the benefit of utilizing the PMU data?

-JK

The advantage of the PMU data is that it's availbale at a high sampling rate and is GPS time-stamped (the data is synchronized). Use of this data will improve monitoring of the grid and it's visualization, as well as operational awareness, state estimation, model validation and "post-mortem" analysis. Some of the major benefits of the use of PMU data are:
- The ability to accurately identify steady-state and transient stability limits;
- The ability to determine optimal control actions for preserving steady-state and transient stability of the system.

However, when we talk of a phasor, a steady state is implied, which any practical powersystem is never in. If for instance frequency always deviates around a nominal value, would the phasor computed by PMU have any meaning? Does PMU update the phasor corresponding to the changed frequency? Also, if zero cross detection of a signal is chosen for measuring its frequency, the frequency update will not be effected until approx. one time period of the signal. How reliable would the PMU phasors be in this situation?