Depends program objectives. Most of my code does not need to be fast, and some even works better if it is slow so it does not pig some resource
Sounds like a lame excuse for shitty code. Code should be fast/efficient, meaning it should get as much done as possible on as few cycles as possible. If efficient code hogs the CPU because it has a great deal of work to do, making the code slow is probably the wrong approach. Try lowering process or thread priority.