What is the outcome when changing the API version of classes and VisualForce pages during deployment?

When changing the API version of classes and VisualForce pages during deployment, the API version will be changed to the specified version in the deployment package. This means that any features or elements that are enabled or deprecated in that version will be applied to the classes and pages being deployed. This allows developers to leverage the latest Salesforce platform features or to maintain compatibility with certain features by specifying an earlier API version.

By manually adjusting the API version, developers can ensure that their code is compatible with the required features of the Salesforce platform and can also control how their code interacts with the platform's evolving capabilities. This control is essential for managing application behavior and ensuring that the deployment runs smoothly without unintended consequences that a mismatch in API version might introduce.