In modern web development, especially when leveraging JavaScript, Promises have become indispensable for managing asynchronous operations. At first glance, the .then() and .finally() methods of JavaScript Promises may look quite similar. 

However, they serve distinct purposes and have different impacts on the Promise chain. This article sheds light on these methods, their characteristics, and how they should be appropriately used.

Contrasting .then() and .finally() in Promise Handling

To the untrained eye, Promise.prototype.then() and Promise.prototype.finally() may look almost identical. However, there are some crucial distinctions that developers should be aware of. The most apparent difference lies in the fact that finally() does not receive any value passed down the Promise chain. Consequently, the value that the Promise resolves to remains unaffected when using finally().

new Promise((fulfill, discard) => fulfill(10)) .then(y => { console.log(y); // 10 return y + 1; }) .finally(z => { console.log(z); // undefined return z + 2; }); // The Promise will resolve to 11

Another distinction pertains to error management. If one opts to delay error handling, the finally() method will execute regardless, whereas then() will not. This behavior is also true when a preceding .catch() throws an exception.

new Promise((fulfill, discard) => discard(0)) .catch(w => { console.log(w); // 0 throw w; }) .then(v => { console.log(v); // Will not execute }) .finally(() => { console.log('finalization'); // 'finalization' });

Scenarios Where .then() and .finally() Shine:

• Response Transformation: .then() is valuable for transforming API responses before they are consumed;
• Resource Cleanup: .finally() is well-suited for releasing resources or clearing timeouts;
• UI Updates: For updating user interface elements based on whether an operation was successful, .then() is often the go-to method;
• Global Error Handling: .finally() could be useful when you want to execute some logic irrespective of the Promise’s resolution.

Best Practices in Using .then() and .finally()

For .then():

• Chaining: Make use of .then()’s chaining ability to make the code more readable and maintainable;
• Error Handling: Use .catch() blocks efficiently with .then() to manage exceptions gracefully.

For .finally():

• No Return Value: Always remember that .finally() does not influence the Promise’s resolved value;
• Cleanup Operations: Use .finally() for cleaning up resources and not for modifying the Promise outcome.

Potential Pitfalls to Avoid:

• Interchanging Methods: Never substitute .then() with .finally() or vice versa unless there’s a compelling reason;
• Overlooking Errors: While using .finally(), ensure that proper error-handling mechanisms are in place;
• Ignoring Promise State: Be conscious of the state of the Promise (resolved/rejected) when using these methods.

Conclusion

Understanding the role and behavior of .then() and .finally() methods in Promises is crucial for efficient asynchronous programming in JavaScript. Although they may appear to function similarly, they have unique characteristics that serve specific needs in the application lifecycle. 

The .then() method is generally used for manipulating the resolved value and chaining additional logic, whereas .finally() is more suited for final cleanup tasks. In short, knowing when and how to use these methods can make a significant difference in how well asynchronous operations are managed in web applications.