Prime example:
Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Dennys Franco
With 87-89 in arm strength and arm accuracy, I'm not surprised that he throws out just over 50% of baserunners. What is less obvious in his stats, however, is how pitifully few baserunners even try to steal 2nd or 3rd. Compared to other catchers in the league, I estimate that there's a 50% reduction (or more) in stolen base attempts.
So with a lower # of SBAs and a much higher % of basestealers caught, a catcher this good
reduces successful stolen bases by the opposition by about 60 or 70%. All those prevented stolen bases represent runners in scoring position, and all those guys who never bothered to steal are on first setting up a GIDP.
Personally, I think defensive catchers are awesome. Just plain awesome.