Flash creates a rich user experience, with all the bells and whistles.

Flash can be used to develop a complete website or cit an be used to put banners in website.

If you are looking for Search Engine optimization in your website than Full Flash websites are not advisable as search engine crawlers dont crawl full flash websites.

There are other tools like real media player and windows media player who provided rich media experience but they can be slowloading compared with Flash.