[ShaBoomer]

From the In-Game Strategy Guide (Hitting Section, Page 4):

"Power swing is most useful when the batter is ahead in the count and confident about his swing. It can help to advance runners from second or third, especially with fewer than two outs. [...]"

"Power swings are harder to time, harder to check, and have less plate coverage than regular swings. They are especially less effective at hitting pitches bordering our outside of the strike zone. But the extra power can turn a deep fly ball into a home run, turn a single into a double, or advance runners extra bases. The drawback is a big increase in misses and strikeouts and a decrease in line drives. The ideal pitch to power swing against is a fastball deep in the strike zone, which is most common on ahead counts"

"Contact Swing is most useful when the batter is behind in the count and not confident about his swing. It can help to avoid strikeouts and even prolong a difficult at-bat into a walk. [...]"

"Contact Swings are easier to time, easier to check, and have more foul coverage than regular swings. They are especially helpful in catching pitches outside of the strike zone that are normally very difficult to get. However these hits do no travel as far as with regular swings and generally are not as valuable for offense."

"Unlike Power Swinging which helps a good hitter achieve extra bases, Contact Swings are mainly for helping weak hitters avoid a strikeout. Situations where this may matter include certain close game situations such as scoring a runner from third with less than two outs. In unique situations, by sacrificing the overall potential for multiple runs you are increasing the chance of a single run to tie or win the game as with a sacrifice bunt. It's best to use Contact Swing sparingly."