When you are making timing corrections to a recording the rhythm of which (in terms of phrasing) is well realized but somewhat imprecise, you will only wish to move the start of one or two words. The automatic length adjustment of neighboring words will be to your advantage in this case, as it will avoid “gaps” opening up between words.
There will also come times, however, where you wish to change the rhythm by, for example, moving a word one sixteenth note backwards but without lengthening the preceding word by the same amount. That is: You want to insert a pause.
In such cases automatic length adjustment is counter-productive, because it means the note you are dragging (without more) will drag the end of the preceding word along with it:
If you want a pause to appear instead, begin by selecting the second note separation tool and then double-click on the transition between the notes:
The usual separation dash then changes to a square bracket to show you that the two words are no longer connected. You can now move either without it affecting the other and thereby create a pause or (something scarcely ever seen in the case of vocals) an overlap:
You can also use this technique of changing “soft” separations (where the notes are connected) to “hard” ones (where they are not) to avoid stretching breaths unnecessarily.