An insert edit, for instance, becomes a trivial operation: simply drag the clip to be inserted onto the overlay track, and trim it as desired. (See The Picture-in-picture tool if you want the second video to appear at reduced size so that only part of the main video is obscured.)
An insert edit on the overlay track. The main video is obscured while the B clip is playing.
In the J-cut and the L-cut, the audio portion of a clip begins a little before (J) or a little after (L) the video. They are often used together to soften the start and end of an inserted clip.
Split editing on the overlay track. The overlay video track has been locked, allowing the B clip’s audio to be trimmed. The main audio can be reduced or muted as needed.