Adobe spells it out. Here’s a summary.

When to Use Progressive Download

Progressive download is a perfect use for hobbyists or websites that have low traffic requirements and only need to deliver short videos. Customers who need advanced features and control over their video delivery—not to mention displaying video to large audiences (for example, several hundred simultaneous viewers), tracking and reporting video viewing statistics, or offering the best video experience—should consider streaming video.

Upload Video to Multiple Sites Automatically