If C * S > R / P, then don't play.
It wouldn't make sense, for instance, for a company like Google to treat all its customers the same way that enterprise SaaS companies treat their more precious customers. S is too big for them. That level of service is manpower intensive.
On the other hand it's probably something you can afford to at the beginning, when you have few customers - an advantage of being a startup, (as I recall being told a few years back, 'You are your own slave labour.')
