As a rule, the leader mostly stays in the slot, leaving it only to make room for the follower to pass by.
The leader almost never makes the follower circle around when passing by; they may go into a common rotational figure when the follower happens to come close, but such figures are usually in a tight position and do not change the overall "slotted" appearance.
[3] The most typical slotted dance is West Coast Swing.
By one theory, the slotted style was born in Hollywood: film directors supposedly wanted to keep the performers in a straight line to keep the profiles of both dancers in sight, which also helps the camera to catch the most action, as opposed to rotational styles, in which much of the time one sees only the back of one dancer with the other dancer hidden completely.
Another story is that during jazz concerts the fans were dancing in the aisles (which are essentially slots) and the style stuck.