Back around 2010 or so, I discovered that if you had a physical PC game that was also in Steam’s store, you could type in the serial number on the game box and it would register and add it to your Steam library.

There were a few older games I owned that had trouble with running well on newer hardware because of the messy manual updates. Did the seriel bumber i to steam and it installed and updated to a smooth running version on steam at no cost.

Yes, this tied the hard copy to the steam account so there was a loss of reselling unless they changed that at some point. But I never bothered with selling used games and these were old enough that nobody wanted them anyway so I got some free use out of something I was almost ready to throw out.