Is there any specific reason we have made the field as inactive? Need to enable this field to use in some script.
wf_activity on task and sys_approval tables will refer back to the workflow activity that triggered the record.
The field has been disabled to prevent users from editing the field on the form or on the list view. In modifying this field would allow users to remove the reference to the workflow activity.
Even if you need to activate it for a reason I would strongly recommend setting it read only so that no unexpected updates are made to this field.
Also please note that this would be deemed as customisation and will need to be maintained by you with future upgrades as well.