CO2 lasers are sheet metal cutting machines.  While some of their function has been replaced by fiber lasers, but they still do have some benefits that fiber alternatives do not.  They can be used to process materials other than metal.  Typically the purchase price will be less, and as a mature technology they’re well understood.  They also potentially provide a better quality cut on thicker (greater than 1") steel plate than Fiber lasers.  On the other hand, they are more expensive to run and maintain, and tend to lose out in speed as well.