One characteristic of Op Amps that limits the performance of low noise and precision circuits is PSRR. The output of the Op Amp is not only a function of the inputs, but also of the power supply. The PSRR of Op Amps is a frequency dependent function, so that the higher the signal frequency, the lower the PSRR is.
In general, the manufacturers provide high fidelity data for PSRR, which might lead to the question of why we should measure it. There are several reasons that we should measure it ourselves.