I'd do it because-
1- stops the chance of unwanted litters, if your frisky fella gets his paws on a willing female
2- chills them out a bit, especially important if they're a hyperactive little fuckwit
He'll hate you for a bit afterwards like, which is understandable- you've cut his nads off ffs
It's been perceived wisdom that it's likely to reduce aggression and make dogs slightly less likely to bugger off as well as being healthier due to risk of cancer but the biggest studies haven't really proven any link to better behaviour and at least one suggests an actual increase in inter- dog aggression. Anecdotally I have to say most people I know that have neutered their dog do seem to think it helps a bit with boisterous dogs but it's not a fix for general misbehaviour.
The rescue centre we got ours from seemed to have a different view- they were convinced that, in females in particular, it had sometimes radically changed the character of the bitch to the point where some were uncontrollably aggressive having previously been placid and with dogs they felt, if anything, it made them likely to be a bit more anxious which slightly increased the risk of fear aggression.
Most vets still recommend it though and advice about when to do it varies considerably.
Sorry- probably more confused now!