I also have not found any benefits to waiting either, although some people claim things such as better muscle/bone development.
There is research showing increased risk factors associated with spay/neuter at a young age (<5.5 months, generally) for things such as osteosarcoma (that one is <1 year), urinary tract infections (females), and hip dysplasia. (On the flip side, there is a decreased risk of mammary tumors if spay occurs before 2.5 years of age.)
Other risk factors seem not to be associated with age at surgery. (This applies to both increased risk, for things such as hemangiosarcoma, hypothyroidism, cognitive disorders, vaccine reactions, etc., and decreased risk, for things such as testicular tumors, pyometra, etc.)
The references and citations for this research has been posted in the forums already, and you can search for the direct source at
www.pubmed.com.
Certainly millions of dogs have been spayed/neutered at 6 months or younger without reports of development of long-term problems; by the same token millions have been left intact without reported developments of those associated problem. It's all a matter of risk-assessment tailored to the individual.
