Do you really need it?

The world of HPC is studded with cutting edge technology, all of it at a price. The question is do you need it?
This sounds like a simple issue, but in reality it's often quite a challenge to determine whether something will provide increased performance for your (or your users) jobs.
To cut a long story short, the most useful thing you can do to come up with the answer is to determine the requirements of your problem space. Are your tasks particularly reliant on disk IO? Do you have a sensitivity to latency? Maybe your cluster is used to run lots of single processor jobs and does not require high MPI performance at all. Once you know this it's easier to cut through the admittedly shiny technology and focus on what would be of most benefit to your environment.