Check out Scylla and its underlying framework Seastar. They expand their reasoning and show the work.

It is definitely not good advice for all things. For workloads that are either end of the CPU/IO spectrum (e.g. almost all waiting on IO or almost all doing CPU work) it can be a huge win as you can get very good L1 cache utilization, are not context-switching and don't need to handle thread synchronization in your code because not state is shared between threads.

For workloads that are a mix of IO and non-trivial CPU work, it can still work but is much, much harder to get right.