I guess many companies just have so much room to save on their AWS bills. So the service quickly pays for itself. It's fine to keep the subscription at least for a while and maybe later switch to periodically model if the only feature it offers is saving.

But usually it's also about visibility. Services like CloudHealth give you much better billing overview than what AWS gives you. Without that data you may have a lot of blind spots and budget management is much harder. I think the long term value is billing visibility even for companies with good AWS experts.

I think the math behind saving algorithms isn't too complicated. It's just hard to get it around your head specially when you have too many resources. So it's not practical to do it without these tools.

You will be surprised how much inefficiency developers can produce. Especially with infrastructure as code it's just too easy to create oversized resources and forget about them.

Many companies also have a lot of inefficiency with their architecture. So it makes sense to outsource savings on EC2 instances to a service like this and let your internal talents to focus on architecture optimizations where you can probably even save more money.