In general we do not want to discard a measurement methodology because of imperfections, because measurement is almost always imperfect, even in a digital world. Instead, we ask that a methodology analyze its sources of measurement error and quantify the corresponding effects. For example, many methodologies include a measurement of elapsed time, necessitating the use of some form of clock.
All clocks have imperfections.
The clocks in computers are sometimes poorly kept simply due to operating system deficiencies, or due to hardware shortcomings. Thus for any measurement involving a clock we would like to know how the clock's inaccuracies affect the measurement. The former is a measurement error, while the latter is generally related to the metric of interest. The trace produced by the filter can then be analyzed to assess exactly when the network traffic occurred, minimizing the effect of measurement host delays, or at least allowing them to be accounted for. Naturally a goal is then to choose a definition that minimizes the propagation and escalation of errors.