The regime change from laminar to turbulent flow is chaotic, so looking at a system in bulk will give you a decent description of the system, looking at any one part of the system will give you a random answer. This becomes problematic at systems boundaries, especially in engineering where we would like to understand the safety factor. Simulation can give you a reasonable starting place, but at the end of the day you still need test articles to see how it performs in reality.

For example, would you consider the three body problem well described? Even if it is, the solution goes chaotic rather quickly.