A) Yes, there are health issues in both male and female animals that can be prevented through spay/neuter.
In female dogs and cats, spaying before the first heat reduces the risk of mammary tumors (breast cancer) by 95% or greater. After one heat, there is still considerable reduction of tumor rates, but no benefit is seen after a third heat. Spaying also eliminates the risk of uterine infection (pyometra).
In male dogs, neutering eliminates BPH (enlarged prostate) and if an intact male dog develops prostate problems, neutering is one of the first treatments. Neutering also reduces the occurrence of certain tumors in male dogs, reduces the risk of developing perineal hernias and decreases urine marking and wandering behaviors.