For the sake of clarity, it's important to make sure your dialogue and voiceover are clear and concise, and make sure that the words flow into one another evenly and smoothly. This deceptively simple audio editing trick can help you achieve just that.
Obviously, the major caveat with this technique is that it is mostly only applicable to voiceovers and dialogue where the character speaking is off screen or whose mouth can't be seen by the audience - say the character whose shoulder we peer over in an OTS shot. It could potentially be used to clean up on-screen dialogue in certain instances where the actor's performance is consistent from take to take, but you'd have to be extremely careful not to throw things out of sync.
With that exception - and it's definitely a major exception - you can use this technique to really fine-tune your voiceovers/off-screen dialogue and dial in the perfect pacing and word delivery for audio performances.