You can extend the careers of good hitters who have slowed down and become a defensive liability later in their careers.
They found places for those players before the DH -- Dick Stuart and Pete Ward are good examples. And their defensive liabilities helped keep things interesting.
You don’t kill a rally when you see the pitcher come to bat, and he’s an almost automatic out.
Like Doug Fister's double yesterday.
The pitcher usually only bats twice a game anyway, and they can be taught to bunt or do something else that is productive for the offense.
A pitchers "at bat" comes up a minimum of 3 times per game, unless his team doesn't have to bat in the bottom of the ninth.