I think in the nfl you can do two guys and pull one off if he was put on early enough in the season . The whole thing needs a little tweaking , but be wary when putting guys on as they might heal faster than what is shown.
For seroius injuries when dealing with reserves they can be cut. I rarely do that . Or The injury is just not severe enough and it's early enough in the season to warrant not putting them on ir (only cause I can't take them back off ). I almost always do that . And in the rare cases of a high future young guy who I will put on ir, just to let him develop more and completely heal. There is plenty of other more detailed senerios but that kinda how I work it in general .
Still, I find little need for the ir . It's a little more important now , but so would be having depth at a balanced number of positions. In tougher leagues FAS (scheme speific)are hard to come by and replacing some one there is not really comparable , but a little closer as well of recent.
I think some elaboration isn't here yet only cause of possible exploits involving tanking that might come along with a guy possibly not warrantin an ir designation .
I definitely wished I had the option many times but really only needed/used it a handful of times in many leagues /seasons