One person can take papers, photograph them without getting excited, return them, and give them away without any scruples; while someone else has to overcome an enormous obstacle.
There were some tragic cases of women whose love was abused, who for a certain time procured important documents or information, not knowing who for, what service they worked for, and for a variety reasons got jailed, were tried and sentenced.
You can't do anything if a person says no. In such a case, there's nothing you can do - unlike the popular cliche that pressure is exerted, or that maybe an unwilling source is done away with.
Most of the results of using technical bugging devices were of little importance for my service. It may have been different in counter-intelligence, where bugs in flats, etc., were used to obtain a lot of information about what counter-intelligence was interested in.