I do wonder how big the use case for suspend/hibernate is in practice. Are there that many services that (a) see infrequent use that justifies this cost reduction and (b) can't just be booted fresh when needed. I could see if there's a lot of compute-intensive data cached, but this could also just be stored in a disk-persistent cache.
We have been using GCP hibernation since 2018 too, but it was alpha back then. The AWS version also had some limitations (it only supposed Amazon Linux at the time) - current prerequisites here: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/hibernat...
We have hundreds of developer K8s clusters that get used during a normal workday and get shutdown later. Because there are many services (each with their own readiness criteria), a cold boot takes a long time until all services stabilize (worst case I've seen was over 30 minutes). With hibernation they can resume where they started off within a couple of minutes. During development it's often the case that one may be doing experiments and changing the current state, so preserving everything is a plus.
If, as it was often the case when it was alpha, hibernation failed, then the normal startup procedure would take place.
We don't use it in production but I don't think it's inconceivable that there are other use-cases where preserving state could shave time in getting resources ready.
This is exactly what we use hibernation for in conjunction with EC2 Warm Pools -- fast autoscaling of services that have long boot times. There's an argument to be made that fixing slow boots should be the "correct" solution, but in large enough organizations, hibernated instances are a convenient workaround to buy you some time to navigate the organizational dynamics (and technical debt) that lead to the slow boot times in the first place.
I have a ci/cd machine that is only useful to have on when I'm actively working on the projects it manages, makes the difference between a few bucks a month and ~$80
It even makes sense if you have on-prem bare metal, with electricity prices being as insane as they are, you'll notice the effect pretty much immediately.