When Flash first landed on the World Wide Web (we still called it that back in those days) it was very popular it it became common for websites that wanted to look "cool" to load a Flash animation when a visitor visted the site. The standard method was to force the use to sit through this animation to convince them of how cool you were.
As time passed it became widely accepted that this practice was, to use the technical term, totally fucked. Despite years of frustrated users screaming at the websites to get that stupid fucking intro out of their way and let them use the site, some sites argue that there are certain cases where a Flash into is still a good idea.
Maybe so. I'm a helpful guy. Really. So I've provided this handy flow chart for all web designers and marketing people to consult before they put a Flash intro in place. Use this and no matter what your product, no matter who your target audience, you will always reach the right decision: