I think each owner needs to look at the research and decide for themselves.
I wasn't going to spay because by this time Ellie was too old for it to prevent mammary cancer...just pyometra. However, her new vet very strongly suggested that it be done and I know she has seen it all. She felt that the risk of pyometra and trying to do an emergency spay on a small dog while not dumping the uterus was quite risky and that spaying before there was a problem would be in Ellie's best interest. I trusted what she was saying and just went with it. I don't regret it at all. Before spay Ellie was getting llumps in her mammary chain.
The vet said they may go away after spay otherwise we have to start talking about cancer. She was right. They went away.