Ok, so let's say the Twins sign one of those guys to a minor league deal, and hope to get lucky.
Ash and Nick pretty much answered, but my take is simple.
If the guy rebounds and looks surprisingly good, you've added another solid option for the rotation and you've added depth, depth to the pen where Mejia and Romero could both help.
If said guy doesn't flash, he goes to Rochester to continue to work while off the 40 man. He can still be released or opt out.
If, at whatever point, said signee looks good, there is the option to trade him, or anyone else, to bring in another asset or two.
All you are doing is bringing in a flier to see if you get lucky and build depth and possibilities.