I doubt it really is one win's worth though. High leverage innings will primarily go to O'Day and Johnson. Rodriguez will likely see less important situations.
I think this is a big part of the reason for bringing him in. The only 2 relievers Buck trusts in high leverage situations are O'day and Johnson. I doubt Rodriguez would be thrown into something immediately, but if he proves to be trustworthy, Buck will have another option to go to which helps out the pen immensely. Overworking those 2 could be disastrous at the end of the season, and there have been signs of this already.