Cloud services don't save you money, they buy you focus.
If you're a larger business, you can probably absorb that risk if it goes wrong. If you're a startup, it could be catastrophic.
However, I also know larger businesses that just simply do not have good ops teams and a cloud provider would outperform all of them.
> Good ops people can cost as much as good developers.
And this is a surprise? They bring a ton of domain specific expertise, good automation experience, and they lift the burden of managing your systems from your developers, so they can work on features and not scaling.