Programmer Nelson Elhage on the importance of software performance:

What is perhaps less apparent is that having faster tools changes how users use a tool or perform a task. Users almost always have multiple strategies available to pursue a goal — including deciding to work on something else entirely — and they will choose to use faster tools more and more frequently. Fast tools don’t just allow users to accomplish tasks faster; they allow users to accomplish entirely new types of tasks, in entirely new ways.
The basic architecture of a system — the high-level structure, dataflow and organization — often has profound implications for performance. [...] If you want to build truly performant software, you need to at least keep performance in mind as you make early design and architectural decisions, lest you paint yourself into awkward corners later on.