This is from a vet statement I found:
I think that most veterinarians think that neutering male dogs is usually a
good idea. It helps with some behavioral problems and it reduces the risk
of benign prostate hypertrophy later in life. It eliminates the possibility
of testicular cancer. It reduces the incidence of fight wounds, hit by car
trauma and other injuries associated with looking for and finding female
dogs in heat. Male dogs are less likely to urine mark if they are neutered.
Neutering also reduces the risk of perianal adenomas ( a tumor that occurs
around the rectum later in life).
Neutering is an irreversible procedure so it is important that everyone
involved in the decision making by comfortable with the choice to neuter.
When there are disagreements it seems acceptable to me to wait, since most
of the benefits do not appear to be affected too much by later neutering.
The exception might be wandering behavior. Once dogs establish a habit of
roaming, for whatever reason motivates them, it is hard to break that
habit. It is better to neuter early when this is likely to be a problem.
Some dogs do gain weight after being neutered. Overall, the difference in
obesity percentages between neutered and intact males is a 5 to 10%
increase in obesity in intact males. This is the only disadvantage, other
than a slight risk of anesthetic problems, that I know of to neutering.
If there are specific reasons for not neutering that people are giving your
daughter, I would be glad to try to find information on those specific
reasons.
Mike Richards, DVM
http://www.vetinfo.com/dneuter.html#Neutering