What is a key characteristic of custom Web Services?

A key characteristic of custom Web Services in the Salesforce context is that they enable developers to expose Apex code as a Web Service. This allows for the creation of web services that other systems can call to execute the Apex code, making it possible for external applications to integrate seamlessly with Salesforce's operations. By exposing specific logic through a web service, organizations can enhance their system interconnectivity, allowing for better data exchange and operational efficiency.

Moreover, when Apex code is exposed as a web service, it provides the ability to handle specific business processes or data manipulations on-demand from external systems. This functionality is crucial for integrating Salesforce with other applications or services, enabling them to interact with Salesforce data and processes programmatically.

In contrast, the nature of custom web services is not limited to asynchronous scenarios, nor is it exclusively based on REST architecture, as they can utilize SOAP-based approaches as well. Additionally, they are not specifically built for batch processing; while batch jobs can interact with web services, that is not a defining characteristic of custom web services themselves.