Breeding soundness exams are absolutely critical.  You will find that out, much to your sorrow, when you have a bull go bad.  If you are running a sire group you might get by, unless the dominant bull is the one that goes bad.  If you are running single bulls it is even more critical.  Bulls that have previously tested good can and do go bad with no external indicators so simply passing a test as a yearling is no guarantee of future performance.  Even if the bull can physically mount a cow and get the job done there is no guarantee that the semen has high enough quality to get the cow bred.  Only when the semen has been properly evaluated can you be sure that the bull is a viable candidate for use.  Not testing a bull prior to use is a very good example of being penny wise and extremely pound foolish.