When should a variable be configured to be available for input in a flow?

A variable should be configured to be available for input in a flow when whatever initiates the flow is intended to set the variable's value. This is essential in situations where a flow is designed to receive data directly from an external source or a triggering process, such as a button click or a record update. By allowing the variable to accept input, the flow can operate on data that is relevant and current, ensuring that the automation meets user or system requirements accurately.

When a flow starts, it's common for inputs to come from the context in which the flow is being invoked. For example, if a flow is launched from a record in Salesforce, the values from that record can be passed to variables as input, enabling the flow to act on that data. Thus, configuring a variable for input guarantees that the flow can work with the specific data it needs from its starting context.

The other options do not align with the concept of configuring a variable for input. The process of changing a variable's value during flow execution or having a variable output data to another variable is a different aspect of flow functionality and does not require the variable to be set as an input variable.