I'm only casually familiar with chemistry, but I used to do research of a similar type (only far worse, of course) related to electromagnetism. You know the ma

I'm only casually familiar with chemistry, but I used to do research of a similar type (only far worse, of course) related to electromagnetism. You know the main mechanisms at work, but that does not mean you can study all the processes. Sometimes it's just that the sheer size of the mathematical model itself is basically impossible to study without a computer. Oftentimes, though, it's the inadequate formulation of a model that doesn't allow you to simulate it. A good simulation is an immensely useful tool. There are phenomenons which you know and can simulate, but you cannot easily measure their parameters while they are happening (e.g. you risk disrupting the phenomenon because of your measurement installation). I imagine this is even more so for chemists. Real-life example from my own research: we worked on tools that helped engineers who designed really high-frequency ICs (think tens of GHz) study things like cross-talk through the substrate. The mechanism itself is basically well-understood, but save for really, really simple structures that are nothing like those in an IC, you can't solve that by hand. Of course, ours were modest achievements, but the point is that this kind of research can open new gates and shouldn't be considered "second-rate".