Well.. the reason is that if you use it too much your scalp can grow accustomed to the treatment and essentially immune it it, and your scalp will no longer react to the light. I don't know how true this claim is but after spending this much on a device i'm going to use it just how they tell me to . But I used it yesterday and thought it was pretty awesome (not that it did anything, just that it felt like I was helping my hair by using it). I've been itching (literally)to use it all day, but i'm gona be patient and use as directed.