Bottlenecks are the most important thing to understand when it comes to optimizing the performance of applications, because they will indicate the points in which any type of throttling occurs. In this section we will talk about how concurrency and parallelism can affect the performance of an algorithm based on whether it's bound to the CPU or to I/O operations.
You aren't always going to need or even benefit from writing concurrent code. Understanding the bottlenecks of your code, how threads and coroutines work, and the differences between concurrency and parallelism is required to be able to make a correct assessment of when and how to implement concurrent software.