There are some examples of projects that use CleanURLs db in its readme but most have not been updated for a long time.

There are plenty of sites that use more than one parameters. It’s true that a lot of sites now use the history API instead of url parameters but you can still find plenty, and you have no garante about the parameters order. Any site with a search page that have a few options will probably use url parameters instead of the history API. It’s easier to parse and will end up being shorter most of the time.

Well for youtube it’s quite easy, there are only 4 useful parameters that I can think of, the video id v, the playlist id list and index if it’s a playlist and the time t if you’re sending a specific time in the video. Everything else can be removed. Here’s what uBlock Origin with the AdGuard URL Tracking filter list:

! Youtube
$removeparam=embeds_referring_euri,domain=youtubekids.com|youtube-nocookie.com|youtube.com
$removeparam=embeds_referring_origin,domain=youtubekids.com|youtube-nocookie.com|youtube.com
$removeparam=source_ve_path,domain=youtubekids.com|youtube-nocookie.com|youtube.com
||youtube.com^$removeparam=pp

There is no logic as to which parameters is useful and which is used for tracking. But there are databases.

Here is the one for the CleanURLs extension and here is the one for the AdGuard URL Tracking filter list (which I recommend everyone should enable in uBlock Origin).