Security reviews. Powerful enough to run multiple VMs to simulate caching server, web server, app server, and database tier while simultaneously recording and as necessary tampering with all network communications while running static and dynamic code inspection tools across multiple VMs. Load it up with some high-end GPUs as well for hash cracking. Memory is a big deal as well. I work with some programs that if you are running anything under 64 GB of RAM you could be waiting all day for results and 256 GB is preferred but can still be sketchy as that may not leave enough for VMs. If you are a researcher doing fuzzing, again, this sort of power is key to reduce a fuzzing run from maybe a month or two on a a high-end laptop to a few minutes.

Running inadequate machines waste time of otherwise expensive engineers. The other day I was giving a live demo of an interception proxy and accidentally clicked on a very large HTTP response. The machine I was using only had 32 GB of RAM so I had to open task manager and kill the app so I could re-start it because the meeting would have been over by the time it loaded due to disk caching.