If you want to know a little about how Tony LaRussa thinks, then Buzz Bissinger's book "Three Nights in August" will be a must-read. David Pinto pointed out this link at NPR, which has an excerpt on Darryl Kile from the book and three audio snippets on LaRussa's decision-making.

The Kile excerpt goes into more detail than I'm comfortable knowing, but it does elaborate on the role of the clubhouse leader. In the Eldred and roster-construction pieces LaRussa makes it clear that he'd rather have a 700-OPS backup "who's thrilled to be here and contribute" than a 750-OPS jerk. The topic isn't discussed, but one potential reason for LaRussa's reliever fetish is that he can construct clear roles that keep everybody happy, which is harder with seven-man and, to a lesser extent, six-man benches. Last year, for example, LaRussa had a heckuva time finding Marlon Anderson a role. I hope Bill Pulsipher's cool with the idea of being a one-out lefty.