Here are a few reasons NOT to neuter:
-if done before one year of age, significantly increases the risk of osteosarcome (bone cancer); this is a common cancer in medium/large and larger breeds with poor prognosis
-increases the risk of cardiac hemangiosarcoma by a factor of 1.6
-triples the risk of hypothyroidism
-increases the risk of progressive geriatric cognitive impairment
-triples the risk of obesity, a common health problem in dogs with many associated health problems
-quadruples the small risk (<0.6%) of prostate cancer
-doubles the small risk (<1%) of urinary tract cancers
-increases the risk of orthopedic disorders
-increases the risk of adverse reactions to vaccinations
http://www.naiaonline.org/pdfs/LongT...uterInDogs.pdf http://www.mmilani.com/commentary-200509.html
I'm not sure 100% of this is true but the second site seems to support it.
The osteosarcoma part seems to be confirmed and hemangiosarcoma.
Please do what you think is best (and study, because the procedure may need to be done later in life anyway) and don't be pressured into anything.
This is for neutering, not spaying.