I personally think it's the cost savings vs "risk" of getting a refurbished iPhone or iPad. For example, a refurbished iPhone may save you, what $100 over a comparable model? To my wife and I, not worth the savings, we rather get new (iPhone or Android phone)
However for our boys who are rough on their iPads and each on their second iPads already, it makes more sense for us to get refurbished. I try to go thru Amazon too for that extra protection of returning if needed.
Again I agree with the second post above, comes down to personal preference, what you're willing to spend, etc