The difficult thing in the Mii-creation of friends is when they have features in their appearance that they are self-conscious about. You as their friend, of course, don't have an issue with those features and, in fact, might even like those features as part of what makes them unique and/or cute, but you also don't want their reaction to you showing their Mii to be a cause for anxiety about their appearance. You can, of course, make a Mii that doesn't have those features, but then you're not only complicit in the act of covering up those features, as if they should those features, the Mii also just feels less like your friend. It becomes a corporate, sanitized version of your friend. After all, that's not your friend, the Mii doesn't have their bald spot/resting bitchface/bodyfat/etc.