API Gateway provides quotas, which let you control the rate at which applications can call your API. Setting a quota lets you specify usage limits to protect your API from an excessive number of requests from calling applications. The excessive requests might have been caused by a simple typo or from an inefficiently designed system that makes needless calls to your API.
Regardless of the cause, blocking traffic from a source once it reaches a certain level is necessary for the overall health of your API. By setting a quota, you ensure that one application cannot negatively impact other applications that use your API.