A bitch that has been speyed (spayed) will never have another season. This means, as mentioned above, no more bleeding, no males hanging around and no ovarian cancer. It also means the risk of mammary tumours is reduced to almost nil. False pregnancy is no longer a worry along with the emotional upset this causes. Pyometra, infection of the womb, is eliminated. This condition affects many entire bitches in middle to late life. If you are lucky you will see the signs early, most cases result in full hysterectomy of an older bitch less able to cope with the risks of surgery. Many people overlook the fact that the bitch is sometimes overcome by the hormones raging through her body and she is the one intent on escape during her receptive days of heat. Any mating if not fully prepared for is an emotional and costly disaster, both for the bitch and pups and for you in time, money and heartache.
At the end of the day why put your dog through the emotional turmoil every six months? Remember that if noticeable false pregnancy appears the bitch may be an emotional mess for up to three months after the season. If not noticeable the bitch still has some degree of hormone imbalance and emotional upset. It is not natural for the species to be in heat over and over and not have the normal repercussions of that, if you get what I mean. If you let nature take it's course you are still creating a situation fraught with problems. In the wild dogs will breed to the food supply - in the domestic situation food is not a problem. Therefore reproduction is quick and succesful. You will end up with lots of healthy pups with no where to go but the local shelters and they already have their hands full.
Unless you bought the bitch with clear plans to breed and have a suitable stud, along with all the medical details and pedigree information for both potential parents, good homes for at least six or seven pups, money to spend that you don't have to worry about and have a clear idea of the health implications for your pet then speying is the best thing all round.
There are so many dogs around the world in need and we, as a species, created this problem situation. It is up to us to solve it and short of banning dog ownership a solution must be found within the dog owner community. Please give all animals that are not vital breeding stock a special gift by taking away half their frustrations and emotional turmoil for life.
Sorry for going on but this is a vital issue and the more dogs owned by the general public in any country, the more problems and conflicts will ensue and the more local and national governments will be pressured into taking action. Save your dogs before it becomes an issue and train, socialise, train and stop puppies being born that have no good homes to go to and train! Spaying and neutering is vital.