Cream is obtained from the dispersion of drops of fat (15 or 30%) in whey. The action of specific lactic bacteria, it thickens and takes on its flavour. Churning (vigorous mixing which joins the drops together and gets rid of the whey) makes cream into butter, which can then be salted.
The benefits: Cream at 30% fat contains 320 Kcal, at 15% 200 Kcal, and at 8% 110 Kcal. Butter is 82% fat and contains around 750 Kcal per 100g. Both are rich in saturated fat, which is harmful to the cardiovascular system when consumed in large quantities. However, they are an excellent source of Vitamin A.
Intake: Obviously butter should be consumed in great moderation (10g per day), especially if you're watching your figure. Cream is less fatty, especially in low fat versions. By all means use it in your cooking to replace other, unhealthier fats.