As I see it, from my own experience, it depends...
I wouldn't see a reason to neuter a single male, but I have an intact one and a spayed doe as free range house bunnies, and my boy can be a PITA to Dotty at some times of the year, following her around and trying to hump her for days. When he was younger he also occasionally sprayed her, with no regard where they were and with very bad aim. If there are any intact does around they go to great lenghts to get to them, I found a bunny from the neighbourhood twice in my fenced in hutch area wooing my girls which, luckily, were locked in the hutches. If an intakt doe is around, he will get to her eventually, and do what rabbits do.
Apart from that and if there are no issues using the litter box I wouldn't see much of a reason to neuter a male.
With does there are different issues. They can have strong instincts, and hormonal swings. After a Myxo outbreak my little black Fury was my house bunny for 8 months, she reduced all plinth to splinters and flakes - wood and PVC alike, started a tunnel straight into the wall until after an inch the bricks stopped her, almost succeded in killing me twice by removing the insulation from power cords, left her mark in places I only found when I moved out, and when spring came she had her first litter of 5 in my kitchen....(I didn't know much about rabbits back then) - she's a happy, 11yo outdoor bunny now.
False pregnancies will occur, and they have can have very strong opinions about hierachy and stuff. Don't know if spaying does much about that, my two spayed does were docile and not dominant anyway.
Then there is the health issue. Although the numbers spread as a deadbeat argument for spaying are IMO blown out of proportion the cancer risk definitly is there, in my opinion more like 20-25% in their lifetime, but that's still a lot. I've had 5 breeding does in 10 years, and I'm pretty sure that was what Magda died of at age 7.
Then there is the risk of pregnancy. Rabbits are good at that, I think there was only a single year when I didn't get at least one surprise litter. One door not properly latched, baby bunnies. A fence not high enough, baby bunnies. A mistake when sexing rabbits - you guessed it: baby bunnies. Once a tiny wild buck squeezed through the fence and knocked up one of my girls. They don't waste a chance.
2 years ago then 7yo Red got pregnant, after being retired for 2 years. Can't praise my vet enough to answer my call on a saturday after I didn't manage to get the stuck kit out, they did an emergency spay and against all odds Red pulled through, still lives with her mother Fury. 10-14 years are a long time for things to happen, and as I said, they don't waste a chance and are ready every second of those years, but when they are too old or were not bred for years the chances get high that they don't survive it.
So, if it's not a breeding doe, I don't see much reason to not spay. Yes, there is a risk, but with an experienced vet it's more in the 1-2% range (talk to your vet about it) and smaller than health risks of intact does, and propably way, way cheaper than treating problems when they pop up later in life. I would say, the sooner the better, the decision doesn't get easier the longer you live with them.
