Even a lightly studded tire will vastly improve your traction and therefore safety. It only takes a tiny patch of ice to cause a bad fall.... and you never know when some motorist will pass or follow you too closely at just that moment. For me that's worth the minor expense and trouble of a tire change a couple times a year. In fact, it could be that the tiny, infrequent, patches of ice are the worst, since you won't be expecting them and will be riding less carefully. Ice can also be hidden under snow, or under a little water... no way I'll go on my bike without the studs when it's below freezing.