I'm one of those people who uses the cellular data toggle several times daily.
My problem is that I have very bad GSM data reception in my house (which I don't really care about - I use Wifi). The problem is that some buggy apps (mainly Whatsapp) decide to use cellular data in some situations even when Wifi is active. This also happens for the push notification connection (I will experience delayed push notifications) and for Siri (it will take her a lot longer to answer).
I know it's unusual to have such bad reception, but my only solution is to disable cellular data when I'm home. The other alternative would be to divert my call to a landline or VoIP line, and enable airplane mode. But that takes even longer to do, and I would miss my regular, non-iMessage texts.
So yes, I'd appreciate such a toggle in control center.