Every business nowadays relies on integrations through REST APIs. It can actually be very costly to not realise when your integrations stop working due to an undetected API issue. Might those API be internally developed and maintained or external API totally out of your control (eg: a bespoke company facing knowledge sharing system, a special dashboard your executives require to monitor daily, your cloud ERP, CRM and accounting software etc.).
When building any software project and its integrations, it is essential to know that the various components of the application can safely rely on fully tested and working back-end APIs. This is especially true when the components might change and quickly evolve over time. The solution to this problem is pretty simple: you should make sure your API’s business logic has fully automated regression testing, so that you know what can break, before every new release.