Can't speak for YT but these sorts of identifiers are used for basically what you said - tracking and analytics in order to make more money, at scale. Social m

Can't speak for YT but these sorts of identifiers are used for basically what you said - tracking and analytics in order to make more money, at scale. Social media sites are concerned with one thing - ads. That ID is probably stored somewhere in their backend. I'm sure 0.1% of users will strip that query param out (literally nobody does lol), but now their server has registered that you created a share link with si=1234 Now your friend Sally opens that link, and they register that this other user opened a share link with si=1234 What happens next is used to make more money.