I assume you're referring to ASF's with that comment. Our rats here are actually very well behaved, and most of them have had access to a wheel at one point or another. Certain ones would use it constantly, and there hasn't been any change to their personality after having it removed.
Our ASF's have also done fine without any wheels. It's definitely a benefit to give them a wheel as it keeps them busy, but I wouldn't say it's a requirement. As far as our ASF's go, we actually haven't had a single fight break out the whole time we've had them.