My first Basenji had 2 heats a year, and then she'd always have a false pregnancy after each heat. And she was bitchy for the month she was in heat… and bitchy for the 2 months she was "pregnant". So that meant, with 2 heats a year, she was bitchy for 6 months out of the year. Talk about a good reason to spay a dog!
And Pat is right, there is no good reason to keep a bitch whole if she doesn't need to be. Never mind just the convenience of it,,,,, Pyometra IS a threat. I had 2 bitches get Pyometra. I lost one, the other was saved with an emergency spay.