It also stops them wanting to stray and find a female, as well as health benefits in later life when uncastrated males can suffer from prostate problems or cancer. If you keep males and females together it certainly makes life easier if they are not to be bred from and if you keep only males, it reduces the amount of dominant aggression you get from the top dog if you get the underdog castrated. In some cases it can reduce the problems associated with general aggression although if this is a learnt behaviour it is very difficult to change it, same with obvious things like lifting their leg indoors.