The honest answer is that there is a risk of being over-committed with reserved instances and savings plans regardless of whether you purchase them yourselves or rely on something like Autopilot to do it. We target RIs specifically because you can sell out of them on the AWS EC2 RI Marketplace which isn't the case with AWS Savings Plans.

Ultimately, cost savings are our business and what our entire team focuses on all day every day. Most everyone on our team has also either worked at AWS or another public cloud provider and knows this stuff inside and out.

While Autopilot looks to maximize savings, it always errs on the side of not overcommitting you. We haven't had a single incident here and have taken both technical and operational steps to ensure this doesn't happen.

An off by one error by vantage makes your company purchase hundreds of not needed 3 year commitments

If it misbehaves and buys too many / the wrong kind of RIs, you will be locked in to a high monthly AWS bill until you can sell the RIs on the AWS RI marketplace, which has a whole bunch of caveats: https://aws.amazon.com/ec2/purchasing-options/reserved-insta...

It could purchase numerous RI's and then find there's no market for selling them.