This scene served several important purposes:
* Introducing the Avengers: It was the first glimpse into the larger Marvel Cinematic Universe (MCU) and the concept of a team of superheroes, setting the stage for future films.
* Teasing the future: It generated immense excitement and anticipation for a potential Avengers movie, which was at the time still a distant dream.
* Connecting the dots: It implied that the events of Iron Man had wider ramifications and that Tony Stark's actions were not isolated.
* Introducing Nick Fury: It introduced a key character who would become a central figure in the MCU, bringing together different heroes and storylines.
Essentially, the post-credits scene of Iron Man was a brilliant piece of marketing and storytelling that hooked audiences and planted the seed for the massive success of the MCU. It established the interconnected nature of the films and hinted at the grander plans that were to come.