One issue I had with Halo 3 was that in Multiplayer, you would run across people that had just created tags using promotional codes, and going into Multiplayer. They may be a 50 on their main tag, but on this tag they were starting over and the match making would pair skills that did not make for a balanced fight.
They ‘could’ set up the system that would require a certain SR level and once reaching that SR level, only they could you compete in Post competitive matches that had an effect on your rank.
It would put an end to that behavior. Honestly, not sure why someone isn’t taking that code and entering it in on their main tag. Doing so adds the free time to the expiration of your main tag.