Why OOTB Roles must be customized?

As we know SharePoint has predefined set of OOB permission levels, i.e.

full control, contribute, designer, and etc. Most of the time these permission doesn't provide us the desired functionality. The most permission level that provide us the exact requirement is Designer role in publishing sites.

For example if we have a approval workflow and assigned specific user to Designer role as approver we need take into account that Desinger role has delete permission. For instance if approver deletes what he need to approve( this is not we are expecting). The solution for this is to edit OOB permissions for desinger role and to prohibit 'delete items' action, or create a new role and we need to pay attention to roles we are using in production system just to avoid such cases