The Why is easy. On an 11 man staff you have 5 starters and 6 relievers. Last year the avg NL pen ate 504 IP or 84 innings per reliever. Grant it, the number is moved around a bit b/c of roster moves, trades, and Sept callups, but that is the pace they are on. If you have a Loogy, they only will throw in the neighborhood of 40 to 45 innings per year. That means that the other 5 guys in the pen go over 90 IP on average. That number is important because most people consider 80 to 85 appearances or 90+ IP for a reliever as keys to major arm problems. There have been a number of studies done on pitchers showing poor performances the years following from tired arm syndrome b/c of abuse in IP as a reliever and in the number of appearences they make. On 12 man staffs where you have 7 relievers, dividing that out is 72 IP per person. Subtracting the 40 to 45, you are on a pace for about 77 IP per pen person, which is more manageable. However, that 12th pitcher comes at a cost b/c you are giving up a position player that can help out if your team is positionally challenged, injury prone, or needs help in the late innings with specific PH duties. The Cubs are pretty well set with versatility in positions. Likewise they have Z and Marquis who can PH in x inning games. The problem for the Cubs are the number of day to day injuries they manage to pile up, the most recent examples being DeRosa, ARam, and Soriano. If you have 1 or 2 people with nagging injuries + 8 you put on the field + the back up catcher, then you only have at most 1 player to pinch hit from either side- which makes the situation to be absolutely perfect for you to use him. If it doesnt work or isnt the right situation, then you have to deal with the consequences. Also double switching or defensive substitutions are very limited. For some 11 is the way to go. For others its 12. I prefer 11 pitchers and 14 hitters. I also think that 3 lefties in our pen is way way overkill.