Hard coding in Apex Salesforce means directly embedding specific values or variables into the code instead of referencing them from a configurable source such as Custom Settings, Custom Metadata, or Custom Labels.

It is generally advisable to avoid hard coding in Apex Salesforce for the following reasons:

1. Maintainability: Hard-coded values are often difficult to maintain and update as they require code changes every time the value needs to be modified. This makes it harder to manage and scale the application over time.

2. Flexibility: Hard-coded values make the application less flexible, as changes cannot be made without editing the code. By using configurable sources such as Custom Settings, Custom Metadata, or Custom Labels, values can be easily modified without requiring code changes.

3. Reusability: Hard-coded values are not reusable and cannot be shared across multiple classes or triggers. By using configurable sources, values can be easily accessed and shared across the entire application.

4. Testing: Hard-coded values make it more difficult to test the application since the values are fixed and cannot be changed during testing. By using configurable sources, values can be easily changed during testing to ensure that the application is working as expected.

In summary, avoiding hard coding in Apex Salesforce can make the application more maintainable, flexible, reusable, and easier to test. It is generally best practice to use configurable sources such as Custom Settings, Custom Metadata, or Custom Labels instead of hard-coded values.