From article on D'backs website:
If he keeps two lefties, Brenly's final cut in the bullpen will be extremely difficult. With Mantei, Myers, Kim/Batista and another lefty -- Greg Swindell, Stephen Randolph or Ron Villone -- in the pen, that would leave just two spots for right-handers Mike Jackson, Bret Prinz and Mike Koplove.
All three have pitched well this spring, but Jackson can become a free agent if he's not on the Opening Day roster, whereas both Prinz and Koplove have minor league options left.
Given past history of organization (remember the catcher quandry of 2002), Jackson will remain on the squad. Koplove fairly sure to remain on roster due to his success for most of last year while Prinz would be candidate to be shuttling back and forth from Tucson when someone proves ineffective or goes down to injury.
BB is likely set on idea of having another lefty in the pen, and Randolph will get close consideration if Swindell continues to get bombed; of course, Swindell could develop a nasty blister and go on the DL for several months.