Convenience is the only serious reason in favor of spying or neutering. However, arguments in favor of desexing dogs are driven by ideology and propaganda. Science always honest, if it is a true hard science. Look here:
http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf
Dogs are individuals and removal of any part of body, especially, reproductive organs, changes them irreversibly. For active dog users it matters. Many of us keep dogs not just as pets, but rather for enjoyment of dog watching in action. For example, you do not need to be not a consumptive hunter to enjoy open field coursing, sledding or herding activity of dogs of your breed. Even dog fights is an important part of their natural interactions. I do not mean pit fights, which are disgusting. I mean fights over a reason, not to death, but fights over female in heat, defending the food, protecting the master, dominance in the pack, etc. Normal dogs do not fight to death. When I selecting a puppy out of a litter, I always watch for the most competitive one, because I like dominant dogs capable to fight well, if necessary. Sheep guarding dogs must fight stray dogs, foxes and wolves attacking sheep. Lead dog in dog sledding team usually left intact and, if you are a breeder, or think about breeding as a possibility, you know that spayed or neutered dogs are lost for this purpose.
