There are many reasons for neutering male cats. Not just for the general cat population. Although that is a very valid reason. If you ever spent time at a shelter and saw the number of animals euthanised because of overpopulation you would realize its validity.
As for reasons for the individual cat some include, preventing the male marking his territory with a very strong and unpleasant odour. It reduces the males urge to wander and to fight with other males. Which reduces the amount of infections an animal contracts. It also prevents certain types of cancer.
There are many shelters and organizations that offer reduced rates or even free neuturing. I suggest that you look for some in your area. The cats are providing a service to you by reducing the rodent population. Neutering prevents future veterinary expenses.

i am also having the same quandry with a farm cat. i have ALWAYS had my animals fixed. always. but it is very true that they come and go so very quickly on a farm. and, when i mentioned fixing the neighborhood stray that lived on my property long before i moved there, everyone had a fit. they liked it that it had impregnated all their cats. seriously. there was almost a revolt. no more neighborhood cats to take care of things. i think in this one situation i may not have this cat fixed.

Farm cats don't always come and go quickly. The first fertile female who was in posession of the barn when we arrived, lasted a few years. Others, not sterilized, lasted longer or shorter times.

Our last female (neutered) was 15 or 16 when she died. The 2 neutered males that replaced her have been here for almost 3 years and are healthy and show no signs of wandering off.

They are hard working animals, deserving of all the care and good food we can provide. We regard them as protection for the barn and feed. They do an excellent job for us and we reward them for it.

I have six cats they are spayed and nutered they are barn/house cats. They catch mice in both places. There are always a couple in the barn and some in the house to cuddle.

:) i definitely feed and protect the farm cat :). i just didn't fix it. i actually built it a tree house so that it could eat in peace and the stray dogs couldn't steal it's food. and i am NOT a cat person. seriously. i was horrified when i realized it live on my property. then figured, well, might as well go with the flow. now my neighbors laugh at the cat with a tree house. okay, even i laugh at myself.

When we bought our house in the country last year, the previous owners asked if we minded them leaving "a couple of cats". Well, the "couple" turned out to be 5: a neutered male, an un-neutered male, and 3 un-spayed females!! Three litters were born before we could take care of business. The first, poor things, must have died from exposure. I made it a point to handle all the other kittens on a daily basis so they wouldn't be wild. Locally they do a free Spay-Neuter Clinic and I figured I'd take them all in to that. Unfortunately it fell through and I ended up having our vet spay/neuter the lot of them! Eleven cats! We've only lost one and we think an owl grabbed her because they all stay pretty close to home. From a personal standpoint, I'd just as soon foot the bill for the spay/neuter. There are always plenty more cats at the Humane Society should our hard-working crew thin out over time! The males are all big babies and we don't have to worry about cat fights because of too many raging hormones. :)