When i was much younger, my friends and I use to joke that you could take a handful of mud, put it in the CD tray, and VLC would open and play the file. Thank you so much VLC team for all you have contributed (and continue to contribute)!
So if you downloaded a random video from the web and want to play it, you need to figure out what player you need to get in order to play it. Back then, a lot of stuff from the web was garbage, corrupted data, named incorrectly, .mpg files that were actually AVI format, etc. So once you found the right player, you had to worry about whether it would play properly with your PC's video card. There were flaky video cards and not all manufacturers had drivers that worked. Then, if the downloaded file was corrupted in any way, chances are the official player would throw its hands up and refuse to play it. Then, once you actually found the right player and verified that it could play the file back, you were still stuck with that player's horrible UI and feature set.
There were brave souls who would download these "codec packs" from super-shady web sites, to act as plug-ins to Windows Media Player, since Microsoft couldn't manage to ship working video playback out of the box for anything but AVI. God knows what else those codec pack installers put on your system.
And reliably playing video directly in your browser? LOL, that would be for another 10 years or so with YouTube.
VLC was a huge breath of fresh air! Maybe it's not so vital now, since proper video playback is "table stakes" on any platform. You can play any video now with one line of Python, right? But we did sorely need it decades ago.