A guy on the ML roster is not going to develop properly if he's not playing. So the idea of "carrying a guy" for a season is counter productive. If you want him to develop, he needs to play regularly.
I use the R5 draft to fill the back end of my roster. I draft them based on current ratings only, and only if they fill an opening on my bench or on the back end (long reliever, mopup, etc) of my pitching staff, or are a marginal upgrade to a veteran that I already have slotted into one of those positions.
Also, if you have a lot of player payroll available, you can also grab the occasional useful veteran in the last year of his contract who somebody else is trying to salary dump. I did this last season with one of my teams. He ended up not providing much value in limited work for me, but he left as a Type B free agent and I will be getting a comp pick for him this season.