Besides the medical reasons for neutering, e.g. testicular, uterine and mammary tumours or to prevent stress due to male rivalry, the main reason for neutering is to prevent unwanted breeding.
If a pet owner does not explicitly want to breed their pet, it is common in Germany for them to have their pet neutered. Of course, it is not required by law that you neuter your pet; it is merely an animal welfare recommendation if there is no intention to breed the pet.
In many countries, neutering is believed to actively contribute to animal welfare as it prevents further animal suffering. Whether or not to neuter an animal is the owner’s decision to make.