It's better than sugar itself. Fewer calories and less impact on blood sugar.
Sugar alcohols are type of carbohydrate called polyols. Many of them are occur naturally in plants like berries and fruits and some of them are directly extracted from sugars.
They have very similar chemical structure as sugars but basically they are not classified as sugars.
I think the confusion arises when some people claim that these are calorie-free but as I stated they do contain calories but not as many as sugar does.