Some mechanisms in a pin try to force a drain. Other mechanisms try to help score points. Some accomplish both.

1. Slings' main purpose is to take ball control away from the flippers, and drive the ball to the OUTSIDE of the playfield (laterally). Slings also add excitement by randomizing ball movement.
2. Occasionally, this random ball movement works in your favor, when they help you make a tough shot or score a point.
3. Once the ball is driven to the outside of the playfield, you need some sort of playfield design to allow for a drain -- thus we find outlanes in most pins.
4. There is player skill that can often interrupt this outlane drain (nudging)

Does that help?
-mof

Yep, 3 of 4 tilt mechanisms are not ones you'd engage by nudging. They are anti-theft / anti-cheating.

1. kick coin door
2. drop the game
3. lift the game

-mof

In 1981, Bally clearly encouraged nudging with the outlane star posts found in a very strange place -- in the outlanes! After you drain the ball, you are given one or two chances to nudge the ball back into play.

Genius.

http://ipdb.org/showpic.pl?id=476&picno=9680&zoom=1

-mof