I have read that Vitamin E is beneficial while taking Claravis. Why?

Whether or not Vitamin E can be beneficial while on isotretinoin is not yet fully clear based on available data. Previously it was felt that Vitamin E could reduce some of the side effects associated with isotretinoin including dry skin and chapped lips and thus some dermatologists recommended Vitamin E supplementation while on isotretinoin. However, more recent data suggests that Vitamin E supplementation may not improve side effects of isotretinoin and will not improve acne severity compared to those not taking Vitamin E supplements. 
With regards to diet while on isotretinoin it is advised to avoid any Vitamin A supplements or limit intake of foods that contain high levels of Vitamin A such as carrots, fish and dark green leafy vegetables. The reason for this is that these may make the side effects of isotretinoin more severe because isotretinoin is itself a Vitamin A derivative. Furthermore, a low fat diet is also recommended while on isotretinoin in order to reduce potential side effect of cholestrol and triglyceride elevation which is commonly seen during isotretinoin therapy.