How much nutritional value is lost when having frozen yogart compared regular yogart?

Probably not much: Nutritionally, if one puts refrigerated yogurt into the freezer and eats it frozen, there should be little difference. However, when the factory makes frozen yogurt, they put in some different ingredients, so one has to read the labels carefully to be sure not to get too much fat or too much sugar. It would be hard for a consumer to tell the quantity of beneficial probiotics in any type of yogurt.

Each has value.: It depends on what value you are looking for. If you want calories they both will do. If you want live cultures then unfrozen yogurt is best. If you are looking for help with weight loss then pick plain yogurt or sugar free. If you want to gain bone mass pick whole milk yogurt but watch the sugar or sweeten it yourself.