What is the primary purpose of the decorator below?

import time
def timer(func):
    def wrapper(*args, **kwargs):
        start_time = time.time()
        result = func(*args, **kwargs)
        end_time = time.time()
        print(f"{func.__name__} took {end_time - start_time:.2f} seconds to run.")
        return result
    return wrapper
@timer
def slow_function():
    time.sleep(2)
    print("Function execution completed.")
slow_function()