My philosophy at the moment is to use HPC only when I've exhausted other possibilities. I think many people jump to HPC prematurely. The simpler approaches are so much cheaper that I think it's usually worthwhile. I'm skeptical of the argument that it's cheaper to use HPC than it is to use more efficient methods in this case, because the more efficient methods are often something like a few days spent reading to find the right equation or existing experimental data vs. at least that much setting up a simulation and longer to run it.
Edit: Bill Rider has a bunch of blog posts that make similar points:
https://wjrider.wordpress.com/2016/06/27/we-have-already-los...
https://wjrider.wordpress.com/2015/12/25/the-unfortunate-myt...
https://wjrider.wordpress.com/2016/05/04/hpc-is-just-a-tool-...
https://wjrider.wordpress.com/2016/11/17/a-single-massive-ca...
https://wjrider.wordpress.com/2014/02/28/why-algorithms-and-...