The pay-as-you-go reductions give you more flexibility about when you make optimisations to your code though and help you handle uncertainty around this.

For example, if I have a new workload that won't fit on existing hardware with AWS, I can either: a) reserve the new instances, or b) not reserve on the assumption I will be able to optimise in the 'near' future.

In practice this is hard to know but AWS forces you to come to a correct decision up front, whereas Google Cloud allows you to not have to answer this up front without being punished later for making the 'wrong' choice.