For me it's the idea of having sunscreen and makeup in one product. I know I have to wear sunscreen, but my face hates it, and my skin especially hates layers of product. Plus, I'm not that into makeup. Sunscreens are usually so greasy, or they sting my eyes, or cause cysts...yuck. But I live in AZ and I'm getting old. I'll fight sun damage and aging tooth and nail!
I've tried Miracle Skin Transformer (greasy, rubs off on everything), Too Faced BB Cream (greasier...makes me look like I haven't washed in a year), Garnier (absolutely a nightmare...full of alcohol and looked like a mask), and a few others. Most of them are clearly made to give skin a white cast, so they look gray and creepy on me.
But - there is one I've been using for a couple of months and I'm pleased with it. It's called Boscia BB Cream. It's super easy. I slap it on in the mornings and I don't have to worry about how I blend it or anything. I don't even have to look in the mirror when rubbing it on. It's got SPF 27, and it kind of "color matches" to my medium olive skin. It gets lighter throughout the day, though, so by evening if I don't touch up with bronzer or something I look like a mime. Aside from that, it has good coverage for covering my dark spots, and it looks as natural as a product like this can look. It shows up white in photos, but for easy, quick day-wear it's really a great product.