Strengths of Black Box Testing

Advantages of Black Box Testing

more effective on larger units of code than glass box testing
tester needs no knowledge of implementation, including specific programming languages
tester and programmer are independent of each other
tests are done from a user's point of view
will help to expose any ambiguities or inconsistencies in the specifications
test cases can be designed as soon as the specifications are complete

Disadvantages of Black Box Testing

only a small number of possible inputs can actually be tested, to test every possible input stream would take nearly forever
without clear and concise specifications, test cases are hard to design
there may be unnecessary repetition of test inputs if the tester is not informed of test cases the programmer has already tried
may leave many program paths untested
cannot be directed toward specific segments of code which may be very complex (and therefore more error prone)
most testing related research has been directed toward glass box testing