The System Administrator will decide if the data field attribute Copy Clear is appropriate for any given field. Basically, if this attribute is set to Yes on any data field than as you create a new contact record using either M (Marked record) or A (Above record) the data in those fields will copy over to the new contact record.
A good example of using the attribute Copy Clear Yes would be the data in address and telephone fields. If you are creating a new contact record from an existing record you would most likely want the address and telephone data to copy over to the new record so that you wouldn't have to retype that data. Any field can be made to be Copy Clear Yes. Some other examples are customer or account number fields. This field attribute only comes into play when you are adding a new contact record based on an existing contact record.