If installations can be avoided then everyone is happy! However this is not always possible. Installations should be as simple as possible, without unnecessary options. A wizard should be used for the options (see 5.2 Use a wizard for product adaptations), when the product is installed.
Changing system files may cause the computer to be unstable. This should be avoided especially if the computer is also used as a technical aid (communication, school work etc.) as these aids may no longer function after the installation. For example a screen reader may not function after updating a screen driver.