When Flash was introduced, it was for creating vector-based animation and basic interactive games. (Kind of like Shockwave but lighter.) It became very popular very quickly because it did lots of neat stuff with very small (vector-based) files and because the browser plugin itself was only a few hundred kilobytes at a time when most people were on dialup and most other plugins (like Shockwave and QuickTime) were several megabytes. Once you downloaded the plugin (just a few minutes) you could
Disc space -- the final frontier!