But downloading a file that’s been encoded somehow is not going to call home to the office of Mr FBI and say they should come raid your computer.

Well of course not, however-

Otherwise it’ll come down to people actually getting their hands on your files to be able to check the content and if you’ve warranted this to happen I’d bet you’ve crossed a few too many lines somehow

Not necessarily. You know where authorities have full control to check electronic devices and even ask for passwords without a warrant? Customs. Random checks have been increasing over the years, and while they still don't happen frequently and aren't really checking for pirated material (unless the pirated material itself is illegal), if they put some time into it and find one with an identifier on it, you could technically get into trouble. Now will they do that? Probably not. They don't have enough time anyways but they could and specially in the US where companies can try to charge people 30000 dollars just for one file, that's not a chance I'm willing to take. Glad to know that the 'identifiers' I've read about are just watermarks tho lmao.