Also important to know that if you're accessing disk, database, or network those are so slow that this stuff probably doesn't matter.

Keep in mind there _may_ be a negative feedback loop there.

If you're building your software in a way that won't be able to perform better with superior disk/db/network performance, then it isn't worthwhile to ever upgrade to a more performant disk/db/network.

If it is possible, make sure your software will actually be faster on a faster disk rather than just testing on a slow disk and thinking "well we're I/O bound anyway, so no need to improve perf".

This is a common fallacy. Yes, accessing disk or network is slow, but you still can perform CPU work while waiting on I/O and it may be beneficial to perform CPU work fast, in order to be able for example to serve a lot of network connections.