Sentence:  While expensive in time and involving a great deal of adaptation on the part of the worker ( in terms of his willingness to leave the sanctity of his office and enter actively into the client 's life ) , techniques of accompaniment were found to <WSD>be</WSD> of tremendous value when in the service of specific preventive objectives . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)