Some discharges can be unintentional and unavoidable/unexpected. What about chambering or cycling a round out of the chamber.
I have seen this happen on an SKS-- it discharged, blowing a hole through 3 apartments and tearing up the walls and carpet. Faulty gun. Luckily nobody was hurt or even heard it (July 4th weekend-- they thought it was fireworks.)
If an internal piece if bad, it could have serious problems as well. A friend of mine was telling me he reassembled his .45, and when he fired the first shot, it emptied the magzine before it would stop... This could have been avoided, but who would have known??? only thing-- he probably did not do a functional check.
Also-- what about the RARE cases of leaving a bullet in the chamber, with a hot barrel-- slight chance that you cook the bullet, and BAM.