I do have a carbon monoxide detector in my home because I have heard how easy it is to die from carbon monoxide poisoning. You can't smell it, so you have no way to know it is there without this detector.
I do not use a carbon monoxide detector in my home. I have heard of people suffering due to ignorance though and it may not be a bad idea to think of it now. It might be worth it if it is not very expensive.
I do not have a carbon monoxide detector in my home. I don't feel that it is absolutely necessary to have one. I have heard of people dying from carbon monoxide, but it is very rare, much more so than a fire.