Apple Final Cut Pro 5 - Manual (Page 657)

322 Part III Fine-Tuning Your Edit
You can achieve the same results using the Selection tool, but with the Selection tool
you sometimes create gaps when you move clips. The Slide tool never creates gaps
(with the exception of sliding the first or last clip).
In the following example, clip B slides to the left. The slide edit changes the Out point
of clip A and the In point of Clip C, but the In and Out points of clip B stay the same.
The duration of clip B does not change, nor does the overall length of the sequence.
Note: To slide a clip between two others, the preceding and following clips must have
handles (extra media beyond the clip In and Out points).
You can perform slide edits by dragging or, for greater precision, by using timecode.
A B C
A B C
Before edit
After edit