Many organizations do not use all change request classes that are provided out-of-the-box (Normal, Standard, Emergency, Latent, Expedited, No Impact). In most cases only three or four of them are used and because of that customers want the other change classes that are not used to be hidden. But since the change class field is a drop-down field, this is a very complex customization because the change class field is present in a lot of forms. In addition, this is not recommended at all because removing OOTB values from a drop-down field might cause some issues with OOTB workflow that checks for or sets specific values in this field.
Therefore, I think that it is a good idea change classes to be made configurable. This could be achieved with an additional field with a menu that shows only specific records from a form (for example, only those records that are enabled). Of course, the field that is currently used for change class will remain on the form but it will be hidden and it will be filled in by workflow based on the value in the other field. Currently similar workflow is used for the status of change requests. The OOTB status field with ID 7 is hidden and there is another field that is shown to the user. The values of this field are dynamic and only the appropriate values are shown based on the current status of the change request.
Furthermore, change classes could be made configurable not globally but based on a company. For example, an option for configuring change classes could be added to the Change Management Rules form.