Okay, so why would John Koronka be the choice to be designated for assignment, when the Rangers needed to call up Desi Relaford?
First of all, this is Koronka's last option. He'll be out of options after this season, so if the Rangers kept him around until 2008, he'd either have to stick on their major league roster out of spring training, or be put on waivers.
Secondly, the Rangers were going to have to clear a 40 man roster spot soon anyway, to activate Joaquin Arias from the 60 day d.l. when the time for his rehab assignment is up. Relaford will likely be removed from the 40 man to make room for Arias, so if Koronka hadn't been DFA'd now, he (or someone) would have been dropped in the near future.
Third, I think the organization has made up their mind that he isn't going to cut it as a major league pitcher. Unlike John Rheinecker, who is great against lefties but struggles against righthanders, Koronka doesn't have a big platoon split that makes him valuable as a LOOGY. And he doesn't have great stuff that he's trying to harness.
He's a guy who will be 27 in a couple of days, and who walks too many batters, and doesn't strike out enough batters, to be a successful major league pitcher.
My guess is that the Rangers will see if they can get a fringey prospect for him, and if they can't, will put him on waivers and hope that he slides through. If he does, great. If not, so be it...not a real big loss.