Can boxed copies of games register on Steam or does it have to be bought digitally? I had a boxed copy of Farcry 2, and was trying to put it on Uplay (I used the code to get it on my computer) and was not able to do so it doesn't recognize the code.
Amazon has a few games super cheap right now in the bundles that I own boxed copies for which is why I'm asking, is it worth just getting the keys for an extra $2.50 to get them on Steam? Is there any actual benefit to it or is it just personal preference?
If they are Steamworks yes, but you would know if they are because they'd require Steam anyhow. In other cases generally no though most relatively recent EA stuff can be registered to Origin.
The whole activating to Uplay and Uplay itself as a game store and client is still relatively new so it's very YMMV on that.