Exception propagation refers to the process by which an exception is passed up the call stack in a program until it is caught and handled. When an exception occurs in a method, and it is not handled within that method, the runtime system propagates it to the method that called it. This process continues up the call stack until the exception is caught by an appropriate handler. If no handler is found, the program will terminate with an error. Exception propagation is essential as it allows exceptions to be caught and handled at the appropriate level of abstraction. For instance, a low-level function might not know how to handle a file-not-found exception appropriately, so it propagates the exception to a higher-level function that has the context to handle it properly, such as displaying an error message to the user. This mechanism ensures that exceptions can be managed flexibly and that code handling different aspects of a program can focus on their specific responsibilities without being cluttered with error-handling code.

Using an excessive number of try-catch blocks in a program can have several negative implications. Firstly, it can make the code less readable and more difficult to maintain. Try-catch blocks, especially when nested or used excessively, can clutter the code, making it harder to understand the main logic of the program. Secondly, overusing exception handling can lead to performance issues. Each try-catch block introduces additional overhead, and in performance-critical applications, this can be detrimental. Additionally, excessive use of exception handling can mask underlying problems in the code. Instead of properly addressing the root causes of exceptions, overuse of try-catch blocks might lead to simply 'catching' exceptions without properly resolving them, potentially hiding bugs and logical errors. A better approach is to use exception handling judiciously, focusing on scenarios where it is genuinely needed and where alternative error-handling strategies are not more appropriate.

Exception handling significantly contributes to the robustness and reliability of a program by providing a mechanism to manage and respond to runtime errors. Without exception handling, any runtime error might cause the program to crash abruptly, leading to loss of data and poor user experience. By implementing exception handling, programmers can anticipate potential errors, handle them gracefully, and ensure that the program continues to run or terminates safely. For example, in file handling operations, if an error occurs while reading a file (like the file not being found), the program can catch this exception and alert the user, instead of crashing. This enhances the user experience and protects the program from unexpected behavior. Moreover, exception handling allows for cleaner code management, as error-handling code can be separated from regular code, making the program easier to maintain and debug. It also aids in resource management, ensuring resources are properly released or closed, thereby preventing resource leaks.

Exceptions should not be used for normal control flow in a program or for handling predictable events that are not truly exceptional. For example, using exceptions to handle user input validation or to control looping constructs is generally considered bad practice. These scenarios are better managed using standard programming constructs like if-else statements or loop controls. Exceptions are intended for handling unforeseen errors and conditions that are outside the normal functioning of the program, such as file not found errors, network timeouts, or resource exhaustion issues. Using exceptions for routine control flow can lead to less efficient, harder-to-read, and maintainable code. Additionally, it can cause performance overhead due to the cost of creating, throwing, and catching exceptions. Therefore, exceptions should be reserved for situations where an error or unexpected condition genuinely disrupts the normal flow of execution, and cannot be anticipated or handled using regular programming constructs.

Checked exceptions are types of exceptions that are checked at compile time. In languages like Java, these are exceptions that the programmer is expected to handle within the code, using try-catch blocks. For example, IOExceptions are checked exceptions, requiring explicit handling in the program. Unchecked exceptions, on the other hand, are not checked at compile time, usually representing errors that reflect some inconsistency in the program's logic, like NullPointerExceptions in Java. Unchecked exceptions often indicate programming bugs and are not necessarily expected to be handled explicitly. The distinction affects exception handling as it determines the programmer's responsibility towards handling the exception. While checked exceptions must be either caught or declared in the method signature, unchecked exceptions can be optionally caught based on the programmer's discretion. This difference influences the design and reliability of the program, ensuring that critical exceptions are not overlooked.