Active probes of network performance represent samples of the underlying performance of a system. Some effort has gone into considering appropriate sampling patterns for such probes: i.e., there has been significant discussion of the importance of sampling using a Poisson process to avoid biases introduced by synchronization of system and measurements. However, there are unanswered questions about whether Poisson probing has costs in terms of sampling efficiency, and there is some misinformation about what types of inferences are possible with different probe patterns. This paper provides a quantitative comparison of two different sampling methods. The paper also shows that the irregularity in probing patterns is useful not just in avoiding synchronization, but also in determining frequency domain properties of a system. The paper provides a firm basis for practitioners or researchers for making decisions about the type of sampling they should use in a particular applications, along wi...