What I was trying to get at is that although the absolute cost of e.g. S3 API calls seems low (you get 1M of them for $5), the marginal cost (cost increase from

What I was trying to get at is that although the absolute cost of e.g. S3 API calls seems low (you get 1M of them for $5), the marginal cost (cost increase from adding one customer) can actually be very large if you make a lot of API calls. So much so that it actually causes serious problems. Cloud pricing can be very sensitive to usage, so in data intensive industries--say security monitoring, where customers may send you 1TB of logs per day--the seemingly low cost of cloud conveniences actually can be very misleading if you're not using them properly. I agree that for example, serving a web page to users where almost everything happens on the client, the marginal cost of running the software is low. But it's not always true, and it's really important to measure and track these costs otherwise you can end up in a bad way. I've seen it happen ;).