Warning! If you delete a field from a catalog, information stored in in this field for ALL records of the associated catalog are lost permanently. You cannot undo this action.
If you delete a field of data type relationship, beware that the corresponding partner field existing in the second catalog will also be deleted. No actual records are effected from this action, but you won't be able to display related records information which were bound to the deleted field.
Example: Suppose that you have a 1 to N type relationship between COMPANIES and PEOPLE catalogs, where you display list of workers under each company record and a single related company is selected for each person record. If you delete the relationship field, the company lookup field from PEOPLE catalog is removed, similarly the "list of workers" displayed under each company record is also removed.