Error.captureStackTrace improves custom error classes by: 1) Creating a proper stack trace for the error, 2) Removing the error class implementation from the stack trace, 3) Making debugging easier by showing only relevant code in the stack trace, 4) Preserving the original throw location, 5) Setting the proper error.stack property, 6) This is a common pattern when creating custom error classes to make them behave more like native errors.