> "If we don't need performance, we don't need caches" feels like a great broader takeaway here.

I don't think this holds true. Caches are used for reasons other than performance. For example, caches are used in some scenarios for stampede protection to mitigate DoS attacks.

Also, the impact of caches on performance is sometimes negative. With distributed caching, each match and put require a network request. Even when those calls don't leave a data center, they do cost far more than just reading a variable from memory. I already had the displeasure of stumbling upon a few scenarios where cache was prescribed in a cargo cult way and without any data backing up the assertion, and when we took a look at traces it was evident that the bottleneck was actually the cache itself.

DoS is a performance problem, if your server was infinitely fast with infinite storage they wouldnt be an issue.