Some male dogs get aggressive when they smell a female in heat. My brother's dog almost tore their door down at those times before he had him neutured. Some female dogs get moody or aggressive when in heat so in a lot of cases it DOES change the behavior. Yes it does take away the need to breed but also the problems that the need to breed can cause. If, however, the spaying or neutering is done on an older mature animal the behavior patterns are already established. Therefore there might not be much change expect is the "need to breed". Are you aquainted with horses? Stallions that get hard to handle are gelded to make them manageable.