This is cheaper than AWS EIP for instances that are using an EIP. It is free for GCP VMs to have a resevered IP and use it vs $3.60/mo for AWS EIP whether its used or not. With GCP, unused reserved IP is $7.20/mo. I can't think of a lot of scenarios where you need to hold on to an IP you're not using for an extended period of time, but I could be wrong.