Studs don't help unless there is enough ice, or hard packed snow to allow the studs to dig into something hard. Then they rock. In other words soft snow or slush is about the same as knobbies. I do use two bikes, one spiked, one with knobbies. Been doing it for at least 10 years. It sure beast changing tires. But, when in doubt, use the studs.
If there is hard, cold, flat ice that is big enough, you will fall without studs eventually. That kind of ice makes stud traction about the same as riding on hard dirt. Really great.