Are cell mutations always bad?

A mutation is a change in the genetic material of an organism.
We’re made from trillions of cells, each with a nucleus
composed of DNA – a set of instructions that tells the cell what
to do. Cells copy themselves with astonishing accuracy, but every now
and then a piece of code is copied incorrectly. This is largely due to
natural radiation interacting with our DNA. This incorrect
piece of code can become a permanent change in the
DNA. Mutations are rarely harmful though. Indeed, most
mutations go unnoticed, as the body has mechanisms to
stop a cell copying itself. Sometimes mutations can benefit
organisms. When a mutation allows an organism to cope
better with an environmental stress, it will be passed on to
future generations through natural selection.