There is no harm with the discount. The harm is only with lock in. Once you reserve instances, you can not change the type (different CPU / memory ratio), region or the number of instances. Once you reserve, you have to pay for your instances 24x7, whether you use it or not. If you require more capacity than reserved, you need to pay the full rate. If you require less capacity, then you need to pay for the unused capacity. You don't have all these headaches with Google Cloud pay per go and automatic discounts. You simply use as many resources as you want and you get the discounts automatically.