Spying boxer

Question
I have two boxers, a female neutered and a male spayed.
A friend of mine has a 16 months old boxer boy and as her and her partner are not planning to breed him she would like to have him neutered.  
However, her partner will have none of it.  Is it a male thing?  Her boxer has recently had a big fight with another unspayed boxer male.
Please let me know the pros and cons of spaying male boxer?  I heard there are agression and cancer reason why they should be spayed. Thank you. Lenka

Answer
Just a quick clarification, while "neutered" actually applies to either sex, it is most typically applied to males.  As well, only females are spayed.

Whether to neuter a male is an individual decision; while the risk of testicular cancer is decreased, the risks of other cancers are increased.  Some aggressions are decreased, and dog-dog aggression is one (it's not so much that the dog himself is less aggressive, as it is that other dogs don't see him as a threat once the testosterone is gone, so don't challenge him in the first place).  However once a dog has been involved in fights, management and behavior modification is required whether the dog is neutered or left intact.  

Neutering is certainly more convenient for the owner, and of course will completely prevent unintended breedings.

A couple of good papers that discuss both the benefits and risk of neutering (and spaying) can be found here:

http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf

http://avmajournals.avma.org/doi/pdfplus/10.2460/javma.231.11.1665