Kubernetes notwithstanding, GCE VM instances are likely to remain an integral part of your organization's cloud strategy for the foreseeable future. Because you are certain to be using a lot of VM instances, you should invest the time to understand how exactly discounts on their usage work.
There are basically two major types of discounts currently available for VMs: sustained use and committed use discounts. Committed use discounts require you to make upfront commitments about how much you will use your VM instances, so if you really know, you will need some specific compute power; by all means, go ahead and make that commitment. Beware, always, of making such commitments. The cloud providers offer such discounts in the hope that users will overestimate their need and end up overpaying.
Sustained use discounts, on the other hand...